Pay per click (PPC) is an advertising model used on search engines, advertising networks, and content websites/blogs, where advertisers only pay when a user actually clicks on an ad to visit the advertiser's website.

Advertisers bid on keywords they believe their target market would type in the search bar when they are looking for a product or service. When a user types a keyword query matching the advertiser's keyword list, or views a page with relevant content, the advertiser's ad may be shown. These ads are called a "Sponsored links" or "sponsored ads" and appear next to, and sometimes, above the natural or organic results on search engine results pages, or anywhere a webmaster/blogger chooses on a content page.

Pay per click ads may also appear on content network websites. In this case, ad networks such as Google AdSense and Yahoo! Publisher Network attempt to provide ads that are relevant to the content of the page where they appear, and no search function is involved.

While many companies exist in this space, Google AdWords, Yahoo! Search Marketing, and Microsoft adCenter are the largest network operators as of 2007. Depending on the search engine, minimum prices per click start at US$0.01 (up to US$0.50), these prices are often referred to as Costs Per Click (CPC). Very popular search terms can cost much more on popular engines. Arguably this advertising model may be open to abuse through click fraud, although Google and other search engines have implemented automated systems to guard against this.