Google AdWords is an online advertising service that places advertising copy above, below, or beside the list of search results Google displays for a particular search query, or it displays it on their partner websites. The choice and placement of the ads is based in part on a proprietary determination of the relevance of the search query to the advertising copy. AdWords has evolved into Google’s main source of revenue. Google’s total advertising revenues were USD $43.7 billion in 2012. AdWords offers pay-per-click (PPC), that is, cost-per-click (CPC) advertising, cost-per-thousand-impressions or cost per mille (CPM) advertising, site-targeted advertising for text, banner, and rich-media ads, and remarking (also known as retargeting). The AdWords program includes local, national, and international distribution. Google’s text advertisements are short, consisting of one headline of 25 characters, two additional text lines of 35 characters each, and a display URL of 35 characters. Image ads can be one of several different Interactive Advertising Bureau (IAB) standard sizes. Sales and support for Google’s AdWords division in the United States is based in Mountain View, California, with major secondary offices in Ann Arbor, Michigan and New York. The third-largest US facility is in Mountain View, California, headquarters. Engineering for Google AdWords is based in Mountain View, California. Google has an active official public help and support community maintained and frequented by highly experienced Adwords users (referred to as “Top Contributors”) and Google employees.