Kayak.com is a travel search engine website based in the United States. Founded in 2004, it aggregates information from over 100 other travel sites and helps users book flights, hotels, cruises, and rental cars. Kayak combines results from online travel agencies, consolidators such as Orbitz and Airfare.com, and other sources such as large hotel chains.

Kayak doesn't sell directly to the consumer; rather, it aggregates results from other sites then redirects the visitor to one of these sites for reservation.Therefore, Kayak.com makes money from pay per click advertising, when the consumer clicks-through to one of the compared websites (For example, when the consumer is redirected to the Orbitz website).

The company was established in January 2004 by the ex-founders of Orbitz, Travelocity, and Expedia. It is headquartered in Norwalk, CT and has an R&D center in Concord, MA. Kayak.com has raised $30 million to date, and its investors include Sequoia Capital (led by Michael Moritz) , America Online, General Catalyst Partners, and Accel Partners. It was named one of TIME Magazine's "50 coolest websites" of 2006.

In late 2007 Kayak bought SideStep, another travel search site.