As we update our index, rankings do naturally fluctuate... sometimes a little, sometimes a lot... and for a great variety of reasons. In Google's early days, we updated our index in large, occasional batches, playfully nicknamed "Google Dances." Nowadays, however, we updated our index incrementally. Typically, this results in subtle changes, but some sites can be affected more significantly. And while Google is moving forward, the web is changing at a frantic pace as well. The changes in your site, combined with the constant content and link updates around the web, also can noticeably affect your site's presence in Google. In some cases, however, a site can fall to a lower ranking because it was determined to violate the Webmaster Guidelines. In such situations, you and ideally an unbiased friend or expert should carefully evaluate your site, identifying and fixing any issues. Note that these violations may have been caused by someone who worked on the site previously, or even a hacker who unscrupulously added sometimes-hidden links to your pages. We frequently send informational notices about webmaster violations through the Message Center in Webmaster Tools, so be sure you've signed up for this free service. We'll talk more about Webmaster Tools later in this presentation.