Each year, Google makes hundreds of changes to search. In 2018, they reported an incredible 3,234 updates — an average of almost 9 per day, and more than 8 times the number of updates in 2009. While most of these changes are minor, Google occasionally rolls out a major algorithmic update (such as Panda and Penguin) that affects search results in significant ways.

For search marketers, knowing when major Google updates happened 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.