Google Algorithm Updates Time to Time History: Arjunseo

Each year, Google changes its search algorithm around 500–600 times. While most of these changes are minor, Google occasionally rolls out a "major" algorithmic update (such as Google Panda and Google Penguin) that affects search results in significant ways.

For search marketers, knowing the dates of these Google updates can help explain changes in rankings and organic website traffic and ultimately improve search engine optimization. Below, we’ve listed the major algorithmic changes that have had the biggest impact on search.

2014 Updates

Page Layout #3 — February 6, 2014

Google "refreshed" their page layout algorithm, also known as "top heavy". Originally launched in January 2012, the page layout algorithm penalizes sites with too many ads above the fold.
Google Updates Its Page Layout Algorithm To Go After Sites "Top Heavy" With Ads (SEL)

2013 Updates

Authorship Shake-up — December 19, 2013

As predicted by Matt Cutts at Pubcon Las Vegas, authorship mark-up disappeared from roughly 15% of queries over a period of about a month. The fall bottomed out around December 19th, but the numbers remain volatile and have not recovered to earlier highs.
Google's December Authorship Shake-up (Moz)
Authorshipocalypse! The Great Google Authorship Purge Has Begun (Virante)

Unnamed Update — December 17, 2013

Almost all global flux trackers registered historically high activity. Google would not confirm an update, suggesting that they avoid updates near the holidays. MozCast also registered a rise in some Partial-Match Domains (PMDs), but the patterns were unclear.
The Biggest SERP Flux Since Penguin 2.0 (Dejan SEO)
Google Denies A Major Update On December 17th (SEL)

Unnamed Update — November 14, 2013

Multiple Google trackers picked up unusual activity, which co-occurred with a report of widespread DNS errors in Google Webmaster Tools. Google did not confirm an update, and the cause and nature of this flux was unclear.
Was There a November 14th Google Update? (Moz)
Was There A Google Update On November 14th? (SER)

Penguin 2.1 (#5) — October 4, 2013

After a 4-1/2 month gap, Google launched another Penguin update. Given the 2.1 designation, this was probably a data update (primarily) and not a major change to the Penguin algorithm. The overall impact seemed to be moderate, although some webmasters reported being hit hard.
Penguin 5, With The Penguin 2.1 Spam-Filtering Algorithm, Is Now Live (SEL)
Google Penguin 2.1 Was A Big Hit (SER)

Hummingbird — August 20, 2013

Announced on September 26th, Google suggested that the "Hummingbird" update rolled out about a month earlier. Our best guess ties it to a MozCast spike on August 20th and many reports of flux from August 20-22. Hummingbird has been compared to Caffeine, and seems to be a core algorithm update that may power changes to semantic search and the Knowledge Graph for months to come.
FAQ: All About The New Google "Hummingbird" Algorithm (SEL)
Some Reports Of An August 21/22 Google Update (SER)

In-depth Articles — August 6, 2013

Google added a new type of news result called "in-depth articles", dedicated to more evergreen, long-form content. At launch, it included links to three articles, and appeared across about 3% of the searches that MozCast tracks.
In-depth articles in search results (Google)
Inside In-depth Articles: Dissecting Google's Latest Feature (Moz)

Unnamed Update — July 26, 2013

MozCast tracked a large Friday spike (105° F), with other sources showing significant activity over the weekend. Google has not confirmed this update.
Was There A Weekend Google Update? (SER)
MozCast Update (Google+)

Knowledge Graph Expansion — July 19, 2013

Seemingly overnight, queries with Knowledge Graph (KG) entries expanded by more than half (+50.4%) across the MozCast data set, with more than a quarter of all searches showing some kind of KG entry.
The Day the Knowledge Graph Exploded (Moz)

Panda Recovery — July 18, 2013

Google confirmed a Panda update, but it was unclear whether this was one of the 10-day rolling updates or something new. The implication was that this was algorithmic and may have "softened" some previous Panda penalties.
Confirmed: Google Panda Update: The "Softer" Panda Algorithm (SER)

Multi-Week Update — June 27, 2013

Google's Matt Cutts tweeted a reply suggesting a "multi-week" algorithm update between roughly June 12th and "the week after July 4th". The nature of the update was unclear, but there was massive rankings volatility during that time period, peaking on June 27th (according to MozCast data). It appears that Google may have been testing some changes that were later rolled back.
Google's "Multi-Week" Algorithm Update (Moz)
Google's Matt Cutts: Multi-Week Update Rolling Out (SER)

Panda Dance — June 11, 2013

While not an actual Panda update, Matt Cutts made an important clarification at SMX Advanced, suggesting that Panda was still updating monthly, but each update rolled out over about 10 days. This was not the "everflux" many people had expected after Panda #25.
Google’s Panda Dance: Matt Cutts Confirms Panda Rolls Out Monthly Over 10 Of 30 Days (SEL)

"Payday Loan" Update — June 11, 2013

Google announced a targeted algorithm update to take on niches with notoriously spammy results, specifically mentioning payday loans and porn. The update was announced on June 11th, but Matt Cutts suggested it would roll out over a 1-2 month period.
Google Payday Loan Algorithm: Google Search Algorithm Update To Target Spammy Queries (SEL)
Google Spam Algorithm For Spammy Queries: Pay Day Loans+ (SER)

Penguin 2.0 (#4) — May 22, 2013

After months of speculation bordering on hype, the 4th Penguin update (dubbed "2.0" by Google) arrived with only moderate impact. The exact nature of the changes were unclear, but some evidence suggested that Penguin 2.0 was more finely targeted to the page level.
Penguin 4, With Penguin 2.0 Generation Spam-Fighting, Is Now Live (SEL)
Penguin 2.0/4 - Were You Jarred and/or Jolted? (SEOmoz)

Domain Crowding — May 21, 2013

Google released an update to control domain crowding/diversity deep in the SERPs (pages 2+). The timing was unclear, but it seemed to roll out just prior to Penguin 2.0 in the US and possibly the same day internationally.
Google Domain Crowding Update: May 2013 (High Position)
Google Domain Clustering Update (Justin Briggs)

"Phantom" — May 9, 2013

In the period around May 9th, there were many reports of an algorithm update (also verified by high MozCast activity). The exact nature of this update was unknown, but many sites reported significant traffic loss.
A Google Update Is Happening (Google: Nothing To Announce Now) (SER)
SEO Findings From Google’s Phantom Update (GSQi)

Panda #25 — March 14, 2013

Matt Cutts pre-announced a Panda update at SMX West, and suggested it would be the last update before Panda was integrated into the core algorithm. The exact date was unconfirmed, but MozCast data suggests 3/13-3/14.
Google's Final Manual Panda Refresh Here? #25 (SER)
Google Panda Update 25 Seems To Have Hit (SEL)

Panda #24 — January 22, 2013

Google announced its first official update of 2013, claiming 1.2% of queries affected. This did not seem related to talk of an update around 1/17-18 (which Google did not confirm).
Google Announces 24th Panda Refresh; Not Related To January 17th (SER)
Google Panda Update Version #24; 1.2% Of Search Queries Impacted (SEL)

2012 Updates

Panda #23 — December 21, 2012

Right before the Christmas holiday, Google rolled out another Panda update. They officially called it a "refresh", impacting 1.3% of English queries. This was a slightly higher impact than Pandas #21 and #22.
Confirmed: A Panda Refresh, Version #23 (SER)

Knowledge Graph Expansion — December 4, 2012

Google added Knowledge Graph functionality to non-English queries, including Spanish, French, German, Portuguese, Japanese, Russian, and Italian. This update was "more than just translation" and added enhanced KG capabilities.
Get smarter answers from the Knowledge Graph from Português to Japanese to Russian (Google)
Google’s Knowledge Graph Expands To More Languages, Including Italian, French, Japanese And Russian (TechCrunch)

Panda #22 — November 21, 2012

After some mixed signals, Google confirmed the 22nd Panda update, which appears to have been data-only. This came on the heels of a larger, but unnamed update around November 19th.
Official Google Panda #22 Update: November 21 (SER)
Confirmed: Google Panda Refresh #22 On November 21st; 0.8% Of Queries Impacted (SEL)

Panda #21 — November 5, 2012

Google rolled out their 21st Panda update, roughly 5-1/2 weeks after Panda #20. This update was reported to be smaller, officially impacting 1.1% of English queries.
Google Releases Panda Update 21, Impacts 1.1% Of US Queries In English (SEL)
Official: Google Panda Refresh On November 5th (Version 21) (SER)

Page Layout #2 — October 9, 2012

Google announced an update to its original page layout algorithm change back in January, which targeted pages with too many ads above the fold. It's unclear whether this was an algorithm change or a Panda-style data refresh.
It’s “Top Heavy 2″ As Google Rolls Out Update To Its Page Layout Algorithm (SEL)
Google Page Layout Algorithm Officially Updated (SER)

Penguin #3 — October 5, 2012

After suggesting the next Penguin update would be major, Google released a minor Penguin data update, impacting "0.3% of queries". Penguin update numbering was rebooted, similar to Panda - this was the 3rd Penguin release.
Google Penguin Update 3 Released, Impacts 0.3% Of English-Language Queries (SEL)
Google Released 3rd Penguin Update: Not Jarring Or Jolting (SER)

August/September 65-Pack — October 4, 2012

Google published their monthly (bi-monthly?) list of search highlights. The 65 updates for August and September included 7-result SERPs, Knowledge Graph expansion, updates to how "page quality" is calculated, and changes to how local results are determined.
Search quality highlights: 65 changes for August and September (Google)

Exact-Match Domain (EMD) Update — September 27, 2012

Google announced a change in the way it was handling exact-match domains (EMDs). This led to large-scale devaluation, reducing the presence of EMDs in the MozCast data set by over 10%. Official word is that this change impacted 0.6% of queries (by volume).
Google's EMD Algo Update - Early Data (SEOmoz)
The EMD Update: Google Issues “Weather Report” Of Crack Down On Low Quality Exact Match Domains (SEL)

Panda #20 — September 27, 2012

Overlapping the EMD update, a fairly major Panda update (algo + data) rolled out, officially affecting 2.4% of queries. As the 3.X series was getting odd, industry sources opted to start naming Panda updates in order (this was the 20th).
20th Google Panda Algorithm Update: Fairly Major (SER)
How Do You Know If Google Panda Or EMD Hurt Your Site? (SER)

Panda 3.9.2 (#19) — September 18, 2012

Google rolled out another Panda refresh, which appears to have been data-only. Ranking flux was moderate but not on par with a large-scale algorithm update.
Google Rolls Out Panda 3.9.2 Refresh (SER)
Panda Update 3.92 Rolling Out (Or Is It Panda 20 Time?) (SEL)

Panda 3.9.1 (#18) — August 20, 2012

Google rolled out yet another Panda data update, but the impact seemed to be fairly small. Since the Panda 3.0 series ran out of numbers at 3.9, the new update was dubbed 3.9.1.
Confirmed: Google Panda 3.9.1 Update (SER)
Google Panda Refresh On August 19th: Version 3.9.1 (SEL)

7-Result SERPs — August 14, 2012

Google made a significant change to the Top 10, limiting it to 7 results for many queries. Our research showed that this change rolled out over a couple of days, finally impacting about 18% of the keywords we tracked.
SERP Crowding & Shrinkage: It's Not Your Imagination (SEOmoz)
7 Is The New 10? Google Showing Fewer Results & More From Same Domain (SEL)

DMCA Penalty — August 10, 2012

Google announced that they would start penalizing sites with repeat copyright violations, probably via DMCA takedown requests. Timing was stated as "starting next week" (8/13?).
An update to our search algorithms (Google)
The Emanuel Update: Google Will Penalize Sites Repeatedly Accused Of Copyright Infringement (SEL)

June/July 86-Pack — August 10, 2012

After a summer hiatus, the June and July Search Quality Highlights were rolled out in one mega-post. Major updates included Panda data and algorithm refreshes, an improved rank-ordering function (?), a ranking boost for "trusted sources", and changes to site clustering.
Search quality highlights: 86 changes for June and July (Google)
Google’s June-July Updates: Site Clustering, Sitelinks Changes & Focus On Page Quality (SEL)

Panda 3.9 (#17) — July 24, 2012

A month after Panda 3.8, Google rolled out a new Panda update. Rankings fluctuated for 5-6 days, although no single day was high enough to stand out. Google claimed ~1% of queries were impacted.
Official: Google Panda 3.9 Refresh (SER)

Link Warnings — July 19, 2012

In a repeat of March/April, Google sent out a large number of unnatural link warnings via Google Webmaster Tools. In a complete turn-around, they then announced that these new warnings may not actually represent a serious problem.
Insanity: Google Sends New Link Warnings, Then Says You Can Ignore Them (SEL)
Google Sends Out New Batch Of Unnatural Link Notifications (SER)

Panda 3.8 (#16) — June 25, 2012

Google rolled out another Panda data refresh, but this appeared to be data only (no algorithm changes) and had a much smaller impact than Panda 3.7.
Official Google Panda Update Version 3.8 On June 25th (SEL)
Google Panda 3.8 Live: June 25th & Refresh Only (SER)

Panda 3.7 (#15) — June 8, 2012

Google rolled out yet another Panda data update, claiming that less than 1% of queries were affect. Ranking fluctuation data suggested that the impact was substantially higher than previous Panda updates (3.5, 3.6).
Confirmed: Google Panda 3.7 Update (SER)
The Bigfoot Update (AKA Dr. Pete Goes Crazy) (SEOmoz)

May 39-Pack — June 7, 2012

Google released their monthly Search Highlights, with 39 updates in May. Major changes included Penguin improvements, better link-scheme detection, changes to title/snippet rewriting, and updates to Google News.
Search quality highlights: 39 changes for May (Google)
Google’s May Updates: Inorganic Backlinks, Page Titles, Fresh Results & More (SEL)

Penguin 1.1 (#2) — May 25, 2012

Google rolled out its first targeted data update after the "Penguin" algorithm update. This confirmed that Penguin data was being processed outside of the main search index, much like Panda data.
Google Releases Penguin Update 1.1 (SEL)

Knowledge Graph — May 16, 2012

In a major step toward semantic search, Google started rolling out "Knowledge Graph", a SERP-integrated display providing supplemental object about certain people, places, and things. Expect to see "knowledge panels" appear on more and more SERPs over time. Also, Danny Sullivan's favorite Trek is ST:Voyager?!
Introducing the Knowledge Graph: things, not strings (Google)
Google Launches Knowledge Graph To Provide Answers, Not Just Links (SEL)

April 52-Pack — May 4, 2012

Google published details of 52 updates in April, including changes that were tied to the "Penguin" update. Other highlights included a 15% larger "base" index, improved pagination handling, and a number of updates to sitelinks.
Search quality highlights: 52 changes for April (Google)
Google’s April Updates: Bigger & Tiered Index, Document Ranking, Sitelink Changes & More (SEL)

Panda 3.6 (#14) — April 27, 2012

Barely a week after Panda 3.5, Google rolled out yet another Panda data update. The implications of this update were unclear, and it seemed that the impact was relatively small.
Confirmed: Panda Update 3.6 Happened On April 27th (SEL)

Penguin — April 24, 2012

After weeks of speculation about an "Over-optimization penalty", Google finally rolled out the "Webspam Update", which was soon after dubbed "Penguin." Penguin adjusted a number of spam factors, including keyword stuffing, and impacted an estimated 3.1% of English queries.
Another step to reward high-quality sites (Google)
The Penguin Update: Google’s Webspam Algorithm Gets Official Name (SEL)
Google Penguin Update Recovery Tips & Advice (SEL)
Two Weeks In, Google Talks Penguin Update, Ways To Recover & Negative SEO (SEL)

Panda 3.5 (#13) — April 19, 2012

In the middle of a busy week for the algorthim, Google quietly rolled out a Panda data update. A mix of changes made the impact difficult to measure, but this appears to have been a fairly routine update with minimal impact.
Google Mocks Me For Missing Panda 3.5 (SER)

Parked Domain Bug — April 16, 2012

After a number of webmasters reported ranking shuffles, Google confirmed that a data error had caused some domains to be mistakenly treated as parked domains (and thereby devalued). This was not an intentional algorithm change.
Dropped In Rankings? Google’s Mistake Over Parked Domains Might Be To Blame (SEL)
Updated: Google Update April 2012? Over SEO Penalty? (SER)

March 50-Pack — April 3, 2012

Google posted another batch of update highlights, covering 50 changes in March. These included confirmation of Panda 3.4, changes to anchor-text "scoring", updates to image search, and changes to how queries with local intent are interpreted.
Search quality highlights: 50 changes for March (Google)
Google’s March Updates: Anchor Text, Image Search, Navigational Search & More (SEL)

Panda 3.4 (#12) — March 23, 2012

Google announced another Panda update, this time via Twitter as the update was rolling out. Their public statements estimated that Panda 3.4 impacted about 1.6% of search results.
Google Says Panda 3.4 Is ‘Rolling Out Now’ (SEL)

Search Quality Video — March 12, 2012

This wasn't an algorithm update, but Google published a rare peek into a search quality meeting. For anyone interested in the algorithm, the video provides a lot of context to both Google's process and their priorities. It's also a chance to see Amit Singhal in action.
Video! The search quality meeting, uncut (Google)

Panda 3.3 (#11) — February 27, 2012

Google rolled out another post-"flux" Panda update, which appeared to be relatively minor. This came just 3 days after the 1-year anniversary of Panda, an unprecedented lifespan for a named update.
Google Confirms Panda 3.3 Update (SEL)
Confirmed: Google Panda 3.3 (SER)

February 40-Pack (2) — February 27, 2012

Google published a second set of "search quality highlights" at the end of the month, claiming more than 40 changes in February. Notable changes included multiple image-search updates, multiple freshness updates (including phasing out 2 old bits of the algorithm), and a Panda update.
Search quality highlights: 40 changes for February (Google)

Venice — February 27, 2012

As part of their monthly update, Google mentioned code-name "Venice". This local update appeared to more aggressively localize organic results and more tightly integrate local search data. The exact roll-out date was unclear.
Understand and Rock the Google Venice Update (SEOmoz)
Google Venice Update – New Ranking Opportunities for Local SEO (Catalyst eMarketing)

February 17-Pack — February 3, 2012

Google released another round of "search quality highlights" (17 in all). Many related to speed, freshness, and spell-checking, but one major announcement was tighter integration of Panda into the main search index.
17 search quality highlights: January (Google)
Google’s January Search Update: Panda In The Pipelines, Fresher Results, Date Detection & More (SEL)

Ads Above The Fold — January 19, 2012

Google updated their page layout algorithms to devalue sites with too much ad-space above the "fold". It was previously suspected that a similar factor was in play in Panda. The update had no official name, although it was referenced as "Top Heavy" by some SEOs.
Page layout algorithm improvement (Google)
Pages With Too Many Ads “Above The Fold” Now Penalized By Google’s “Page Layout” Algorithm (SEL)

Panda 3.2 (#10) — January 18, 2012

Google confirmed a Panda data update, although suggested that the algorithm hadn't changed. It was unclear how this fit into the "Panda Flux" scheme of more frequent data updates.
Confirmed: Google Panda 3.2 Update (SEW)
Google Panda 3.2 Update Confirmed (SEL)

Search + Your World — January 10, 2012

Google announced a radical shift in personalization - aggressively pushing Google+ social data and user profiles into SERPs. Google also added a new, prominent toggle button to shut off personalization.
Search, plus Your World (Google)
Real-Life Examples Of How Google’s “Search Plus” Pushes Google+ Over Relevancy (SEL)

January 30-Pack — January 5, 2012

Google announced 30 changes over the previous month, including image search landing-page quality detection, more relevant site-links, more rich snippets, and related-query improvements. The line between an "algo update" and a "feature" got a bit more blurred.
30 search quality highlights - with codenames! (Google)
Google Announces “Megasitelinks,” Image Search Improvements & Better Byline Dates (SEL)

2011 Updates

December 10-Pack — December 1, 2011

Google outlined a second set of 10 updates, announcing that these posts would come every month. Updates included related query refinements, parked domain detection, blog search freshness, and image search freshness. The exact dates of each update were not provided.
Search quality highlights: new monthly series on algorithm changes (Google)
Google: Parked Domains, Scraper Sites Targeted Among New Search Changes (SEL)

Panda 3.1 (#9) — November 18, 2011

After Panda 2.5, Google entered a period of "Panda Flux" where updates started to happen more frequently and were relatively minor. Some industry analysts called the 11/18 update 3.1, even though there was no official 3.0. For the purposes of this history, we will discontinue numbering Panda updates except for very high-impact changes.
Google Panda 3.1 Update: 11/18 (SER)

10-Pack of Updates — November 14, 2011

This one was a bit unusual. In a bid to be more transparent, Matt Cutts released a post with 10 recent algorithm updates. It's not clear what the timeline was, and most were small updates, but it did signal a shift in how Google communicates algorithm changes.
Ten recent algorithm changes (Google)
Improved Snippets, Rank Boost For “Official” Pages Among 10 New Google Algorithm Changes (SEL)

Freshness Update — November 3, 2011

Google announced that an algorithm change rewarding freshness would impact up to 35% of queries (almost 3X the publicly stated impact of Panda 1.0). This update primarly affected time-sensitive results, but signalled a much stronger focus on recent content.
Giving you fresher, more recent search results (Google)
Google Search Algorithm Change For Freshness To Impact 35% Of Searches (SEL)

Query Encryption — October 18, 2011

Google announced they would be encrypting search queries, for privacy reasons. Unfortunately, this disrupted organic keyword referral data, returning "(not provided)" for some organic traffic. This number increased in the weeks following the launch.
Making search more secure (Google)
Google Hides Search Referral Data with New SSL Implementation (SEOmoz)

Panda "Flux" (#8) — October 5, 2011

Matt Cutts tweeted: "expect some Panda-related flux in the next few weeks" and gave a figure of "~2%". Other minor Panda updates occurred on 10/3, 10/13, and 11/18.
Taking a Closer Look at the Google’s Panda 2.5 “Flux” (SEL)
“Minor” Google Panda Update On November 18th (SEL)

Panda 2.5 (#7) — September 28, 2011

After more than month, Google rolled out another Panda update. Specific details of what changed were unclear, but some sites reported large-scale losses.
Confirmed: Google Panda 2.5 Update Arrived This Week (SEL)
Google Panda 2.5: Losers Include Today Show, The Next Web; Winners Include YouTube, Fox News (SEL)

516 Algo Updates — September 21, 2011

This wasn't an update, but it was an amazing revelation. Google CEO Eric Schmidt told Congress that Google made 516 updates in 2010. The real shocker? They tested over 13,000 updates.
Eric Schmidt's Congressional Testimony (SEL)

Pagination Elements — September 15, 2011

To help fix crawl and duplication problems created by pagination, Google introduced the rel="next" and rel="prev" link attributes. Google also announced that they had improved automatic consolidation and canonicalization for "View All" pages.
Pagination with rel=“next” and rel=“prev” (Google)
Google Provides New Options for Paginated Content (SEL)

Expanded Sitelinks — August 16, 2011

After experimenting for a while, Google officially rolled out expanded site-links, most often for brand queries. At first, these were 12-packs, but Google appeared to limit the expanded site-links to 6 shortly after the roll-out.
The evolution of sitelinks: expanded and improved (Google)
Official: Google Sitelinks Expands To 12 Pack (SEL)

Panda 2.4 (#6) — August 12, 2011

Google rolled Panda out internationally, both for English-language queries globally and non-English queries except for Chinese, Japanese, and Korean. Google reported that this impacted 6-9% of queries in affected countries.
High-quality sites algorithm launched in additional languages (Google)
Google’s Panda Update Launches Internationally in Most Languages (SEL)

Panda 2.3 (#5) — July 23, 2011

Webmaster chatter suggested that Google rolled out yet another update. It was unclear whether new factors were introduced, or this was simply an update to the Panda data and ranking factors.
Official: Google Panda 2.3 Update Is Live (SEL)
A Holistic Look at Panda with Vanessa Fox (Stone Temple)

Google+ — June 28, 2011

After a number of social media failures, Google launched a serious attack on Facebook with Google+. Google+ revolved around circles for sharing content, and was tightly integrated into products like Gmail. Early adopters were quick to jump on board, and within 2 weeks Google+ reached 10M users.
Introducing the Google+ project: Real-life sharing, rethought for the web (Google)
Larry Page On Google+: Over 10 Million Users, 1 Billion Items Being Shared Per Day (TechCrunch)

Panda 2.2 (#4) — June 21, 2011

Google continued to update Panda-impacted sites and data, and version 2.2 was officially acknowledged. Panda updates occurred separately from the main index and not in real-time, reminiscent of early Google Dance updates.
Official: Google Panda Update 2.2 Is Live (SEL)
Why Google Panda Is More A Ranking Factor Than Algorithm Update (SEL)

Schema.org — June 2, 2011

Google, Yahoo and Microsoft jointly announced support for a consolidated approach to structured data. They also created a number of new "schemas", in an apparent bid to move toward even richer search results.
Google, Bing & Yahoo Unite To Make Search Listings Richer Through Structured Data (SEL) What is Schema.org? (Schema.org)

Panda 2.1 (#3) — May 9, 2011

Initially dubbed “Panda 3.0”, Google appeared to roll out yet another round of changes. These changes weren’t discussed in detail by Google and seemed to be relatively minor.
It’s Panda Update 2.1, Not Panda 3.0, Google Says (SEL)
Google Panda 3.0 (SERoundtable)

Panda 2.0 (#2) — April 11, 2011

Google rolled out the Panda update to all English queries worldwide (not limited to English-speaking countries). New signals were also integrated, including data about sites users blocked via the SERPs directly or the Chrome browser.
High-quality sites algorithm goes global, incorporates user feedback (Google)
Panda 2.0: Google Rolls Out Panda Update Internationally & Incorporates Searcher Blocking Data (SEL)

The +1 Button — March 30, 2011

Responding to competition by major social sites, including Facebook and Twitter, Google launched the +1 button (directly next to results links). Clicking [+1] allowed users to influence search results within their social circle, across both organic and paid results.
Recommendations when you want them (Google)
Meet +1: Google's Answer To The Facebook Like Button (SEL)

Panda/Farmer — February 23, 2011

A major algorithm update hit sites hard, affecting up to 12% of search results (a number that came directly from Google). Panda seemed to crack down on thin content, content farms, sites with high ad-to-content ratios, and a number of other quality issues. Panda rolled out over at least a couple of months, hitting Europe in April 2011.
The 'Panda' That Hates Farms: A Q&A With Google's Top Search Engineers (Wired)
Google's Farmer/Panda Update: Analysis of Winners vs. Losers (SEOmoz)

Attribution Update — January 28, 2011

In response to high-profile spam cases, Google rolled out an update to help better sort out content attribution and stop scrapers. According to Matt Cutts, this affected about 2% of queries. It was a clear precursor to the Panda updates.
Algorithm Change Launched (Matt Cutts)
Latest Google Algorithm change (Search News Central)

Overstock.com Penalty — January 2011

In a rare turn of events, a public outing of shady SEO practices by Overstock.com resulted in a very public Google penalty. JCPenney was hit with a penalty in February for similar bad behavior. Both situations represented a shift in Google's attitude and foreshadowed the Panda update.
Google Penalizes Overstock for Search Tactics (WSJ)
Overstock.com's Google Rankings - Too Good? (WMW)

2010 Updates

Social Signals — December 2010

Google and Bing confirmed that they use social signals in determining ranking, including data from Twitter and Facebook. Matt Cutts confirmed that this was a relatively new development for Google, although many SEOs had long suspected it would happen.
What Social Signals Do Google & Bing Really Count? (SEL)
Google Webmaster Video Reconfirms Use Of Social Signals (SEL)

Negative Reviews — December 2010

After an expose in the New York Times about how e-commerce site DecorMyEyes was ranking based on negative reviews, Google made a rare move and reactively adjusted the algorithm to target sites using similar tactics.
A Bully Finds a Pulpit on the Web (NY Times)
Being bad to your customers is bad for business (Google)

Instant Previews — November 2010

A magnifying glass icon appeared on Google search results, allowing search visitors to quickly view a preview of landing pages directly from SERPs. This signaled a renewed focus for Google on landing page quality, design, and usability.
Beyond Instant Results: Instant Previews (Google)

Google Instant — September 2010

Expanding on Google Suggest, Google Instant launched, displaying search results as a query was being typed. SEOs everywhere nearly spontaneously combusted, only to realize that the impact was ultimately fairly small.
About Google Instant (Google)
Google Instant: Fewer Changes to SEO than the Average Algo Update (SEOmoz)

Brand Update — August 2010

Although not a traditional algorithm update, Google started allowing the same domain to appear multiple times on a SERP. Previously, domains were limited to 1-2 listings, or 1 listing with indented results.
Google Search Results Dominated By One Domain (SEL)

Caffeine (Rollout) — June 2010

After months of testing, Google finished rolling out the Caffeine infrastructure. Caffeine not only boosted Google's raw speed, but integrated crawling and indexation much more tightly, resulting in (according to Google) a 50% fresher index.
Our new search index: Caffeine (Google)
Google’s New Indexing Infrastructure “Caffeine” Now Live (SEL)

May Day — May 2010

In late April and early May, webmasters noticed significant drops in their long-tail traffic. Matt Cutts later confirmed that May Day was an algorithm change impacting the long-tail. Sites with large-scale thin content seemed to be hit especially hard, foreshadowing the Panda update.
Google Search Results Dominated By One Domain (SEL)
Video: Google's Matt Cutts On May Day Update (SERoundtable)

Google Places — April 2010

Although "Places" pages were rolled out in September of 2009, they were originally only a part of Google Maps. The official launch of Google Places re-branded the Local Business Center, integrated Places pages more closely with local search results, and added a number of features, including new local advertising options.
Google Local Business Center Becomes "Google Places" (SEL)
Introducing Google Places (Google)