An edit-a-thon (sometimes written editathon) is an event where some editors of online communities such as Wikipedia, OpenStreetMap (also known as a "mapathon"), and LocalWiki edit and improve a specific topic or type of content. The events typically include basic editing training for new editors and may be combined with a more general social meetup. The word is a portmanteau of "edit" and "marathon". An edit-a-thon can either be "in-person" or online or a blended version of both. If it is not in-person, it is usually called a "virtual edit-a-thon" or "online edit-a-thon".

Wikipedia edit-a-thons have taken place at Wikimedia chapter headquarters; accredited educational institutions, including Sonoma State University, Arizona State University, Middlebury College, and the University of Victoria; scientific research institutions such as the Salk Institute for Biological Sciences; and cultural institutions, such as museums or archives.

Several Wikipedia edit-a-thons have been held during the COVID-19 pandemic adhering to social distancing measures. These events have been held online using synchronous voice and video chat as well as through asynchronous message boards and forums.

The events have included topics such as cultural heritage sites, museum collections, women's history, art, feminism, narrowing Wikipedia's gender gap, and social justice issues.

Women, African Americans, and members of the LGBT community are using edit-a-thons to bridge the gap in Wikipedia's sexual and racial makeup and to challenge the under-representation of Africa-related topics.

Some Wikipedia edit-a-thons have been organized by Wikipedians in residence. The OpenStreetMap community has also hosted several edit-a-thons.