Many companies exist in this space, Google Ad Words, Yahoo! Search Marketing, and Microsoft adCenter are the largest network operators. Minimum prices per click, often referred to as Costs Per Click (CPC), vary depending on the search engine, with some as low as $0.01. Very popular search terms can cost much more on popular engines.

When a user searches for a particular word or phrase, the list of advertiser links appears in order of the amount bid. Keywords, also referred to as search terms, are the very heart of pay per click advertising. The terms are guarded as highly valued trade secrets by the advertisers, and many firms offer software or services to help advertisers develop keyword strategies. Content Match, will distribute the keyword ad to the search engine's partner sites and/or publishers that have distribution agreements with the search engine company.

PPC Keyword search engines include: Google AdWords, Yahoo! Search Marketing, and Microsoft adCenter, Ask, LookSmart, Miva, Yandex and Baidu.

Paid Inclusion
Paid inclusion is a search engine marketing method in itself, but also a tool of search engine optimization, since IBP Technologies can test out different approaches to improving ranking, and see the results often within a couple of days, instead of waiting weeks or months. Paid inclusion is a search engine marketing product where the search engine company charges fees related to inclusion of websites in their search index. Paid inclusion products are provided by most search engine companies, the most notable exception being Google.