Yahoo! Search is a web search engine, owned by Yahoo!. Originally, "Yahoo! Search" merely referred to an interface, Yahoo! provided, which would pass on queries to another search engine "behind the scenes" (most recently Google), and display them to the user, under the Yahoo! brand. Originally, none of the actual web crawling and storage/retrieval of data was done by Yahoo! itself.

Seeking to provide its own search engine results, Yahoo! acquired other companies with their own search engines. In 2002, it bought Inktomi, a "behind the scenes" search engine, whose results are shown on other companies' web sites. In 2003, it bought Overture Services, Inc., which owned the AlltheWeb and AltaVista search engines. Initially, even though it owned multiple search engines, it didn't use them on the main Yahoo.com web site, but kept using Google's search engine for its results.

However, starting in 2004, Yahoo! Search became an original web crawler-based search engine, with a reinvented crawler called Yahoo! Slurp. Yahoo! Search combined the capabilities of search engine companies it had acquired, with its existing research, and put them into a single search engine. Its new search engine results were included in all of Yahoo's sites that had a web search function. It also started to sell its search engine results to other companies, to show on their web sites. Its relationship with Google was terminated at that time, with the former partners becoming each other's main competitors.