The handful of search engines that, between them, handle the overwhelming majority of global search volume. Each reached that position through a different combination of technology, distribution, and regulatory circumstance.
What qualifies an engine for this category isn't technology so much as reach: these are the engines that serve as the default, or near-default, search experience for a large share of the world's internet users, typically through owning the browser, operating system, or regulatory environment that puts them in front of users automatically.
Google has held the largest share of global search since the early 2000s, built originally on the PageRank link-analysis algorithm and now incorporating machine learning throughout its ranking systems, from RankBrain to AI Overviews. Its scale and revenue from Google Ads have historically funded a level of continuous ranking-quality investment that no competitor has matched. See Google and PageRank for the full history.
Microsoft's search engine holds a distant but durable second place globally, aided substantially by being the default search engine in Windows and the Edge browser. Bing has invested heavily in AI integration through Copilot, and its index also licenses out to several other engines in this directory, including Yahoo! and Ecosia.
Yahoo! began in 1994 as one of the first curated web directories (see The Directory Era) and remains a widely used search portal today, though its results are now largely powered by Bing's index under a long-standing search partnership rather than an independent Yahoo!-built index.
Baidu holds the dominant share of search within China, operating under China's domestic regulatory and content framework and largely separate from the global search ecosystem that Google, Bing, and their derivatives occupy. It remains one of the largest search engines in the world by query volume despite limited use outside China.