AdWords is Google's flagship advertising product and main source of revenue ($16.4 billion in 2007) . AdWords offers pay-per-click (PPC) advertising, and site-targeted advertising for both text and banner ads. The AdWords program includes local, national, and international distribution. Google's text advertisements are short, consisting of one title line and two content text lines. Image ads can be one of several different Interactive Advertising Bureau (IAB) standard sizes.

Google's AdWords division is based in Ann Arbor, Michigan, the company's third-largest facility behind its Mountain View, California, headquarters and New York City office.

Pay-Per-Click advertisements (PPC)

Advertisers specify the words that should trigger their ads and the maximum amount they are willing to pay per click. When a user searches Google's search engine on www.google.com or the relevant local/national google server (e.g. www.google.fr for France), ads (also known as creatives by Google) for relevant words are shown as "sponsored links" on the right side of the screen, and sometimes above the main search results.

The ordering of the paid listings depends on other advertisers' bids (PPC) and the "quality score" of all ads shown for a given search. The quality score is calculated by historical click-through rates, relevance of an advertiser's ad text and keywords, an advertiser's account history, and other relevance factors as determined by Google. The quality score is also used by Google to set the minimum bids for an advertiser's keywords1. The minimum bid takes into consideration the quality of the landing page as well, which includes the relevancy and originality of content, navigability, and transparency into the nature of the business 2. Though Google has released a list of full guidelines for sites 3, the precise formula and meaning of relevance and its definition is in part secret to Google and the parameters used can change dynamically.

The auction mechanism that determines the order of the ads has been called a "generalized second price" auction. It is similar to the Vickrey auction, but is not equivalent to the Vickrey-Clarke-Groves (VCG) mechanism and hence truth telling is not an optimal strategy.

Placement targeted advertisements (formerly Site-Targeted Advertisements)

In 2003 Google introduced site-targeted advertising. Using the AdWords control panel, advertisers can enter keywords, domain names, topics, and demographic targeting preferences, and Google places the ads on what they see as relevant sites within their content network. If domain names are targeted, Google also provides a list of related sites for placement. Advertisers may bid on a cost per impression (CPM) or cost per click (CPC) basis for site targeting 4.