AOL (stylized as Aol., formerly a company known as AOL Inc. and originally known as America Online) is an American web portal and online service provider based in New York City. It is a brand marketed by the current incarnation of Yahoo! Inc.

The service traces its history to an online service known as PlayNET. PlayNET licensed its software to Quantum Link (Q-Link), who went online in November 1985. A new IBM PC client launched in 1988, eventually renamed as America Online in 1989. AOL grew to become the largest online service, displacing established players like CompuServe and The Source. By 1995, AOL had about three million active users.

AOL was one of the early pioneers of the Internet in the early-1990s, and the most recognized brand on the web in the United States. It originally provided a dial-up service to millions of Americans, pioneered instant messaging, and in 1993 began adding internet access. In 1998, AOL purchased Netscape for US$4.2 billion. In 2001, at the height of its popularity, it purchased the media conglomerate Time Warner in the largest merger in U.S. history. AOL rapidly shrank thereafter, partly due to the decline of dial-up and rise of broadband. AOL was eventually spun off from Time Warner in 2009, with Tim Armstrong appointed the new CEO. Under his leadership, the company invested in media brands and advertising technologies.

On June 23, 2015, AOL was acquired by Verizon Communications for $4.4 billion. On May 3, 2021, Verizon announced it would sell Yahoo and AOL to private equity firm Apollo Global Management for $5 billion. On September 1, 2021, AOL became part of the new Yahoo! Inc.