Stack Overflow is a question-and-answer website for computer programmers. Created in 2008 by Jeff Atwood and Joel Spolsky, it is the flagship site of the Stack Exchange Network. Stack Overflow features questions and answers on certain computer programming topics, and was created to be a more open alternative to earlier question-and-answer websites such as Experts-Exchange. The website was sold to Prosus, a Netherlands-based consumer-internet conglomerate, on 2 June 2021 for $1.8 billion.

Stack Overflow serves as a platform for users to ask and answer questions, and, through membership and active participation, to vote questions and answers up or down similar to Reddit and edit questions and answers in a fashion similar to a wiki. Users of the website can earn reputation points and "badges"; for example, a person is awarded 10 reputation points for receiving an "up" vote on a question or an answer to a question, and can receive badges for their valued contributions, which represents a gamification of the traditional Q&A website. Users unlock new privileges with an increase in reputation like the ability to vote, comment, and even edit other people's posts.

As of June 2025, Stack Overflow has over 29 million registered users, and has received over 24 million questions and 36 million answers. The site and similar programming question-and-answer sites have globally mostly replaced programming books for day-to-day programming reference in the 2000s, and today are an important part of computer programming. Based on the type of tags assigned to questions, the top eight most-discussed topics on the site are JavaScript, Java, C#, PHP, Android, Python, jQuery, and HTML.