Lawrence Mark Sanger (/ˈsæŋər/ ^ⓘ; born July 16, 1968) is an American Internet project developer and philosopher who co-founded Wikipedia, along with Jimmy Wales. Sanger coined the name Wikipedia and provided initial drafts for many of its early guidelines, including the "Neutral point of view" and "Ignore all rules" policies. Prior to Wikipedia, he was the editor-in-chief of Nupedia, another online encyclopedia and the predecessor of Wikipedia. He later worked on other encyclopedic projects, including Encyclopedia of Earth, Citizendium, and Everipedia, and advised the nonprofit American political encyclopedia Ballotpedia. Sanger's other interests include theology and philosophy such as epistemology, early modern philosophy, and ethics. He taught philosophy at one of his alma maters, Ohio State University.

While in college, Sanger began using the Internet for educational purposes and joined the online encyclopedia Nupedia as editor-in-chief in 2000. Disappointed with the slow progress of Nupedia, Sanger proposed using a wiki to solicit and receive articles to put through Nupedia's peer-review process; this change led to the development and launch of Wikipedia in 2001. Sanger continued to serve as Nupedia's editor-in-chief and as an active contributor to Wikipedia in its first year, but he was laid off and left the project in March 2002. Sanger's status as a co-founder of Wikipedia has been questioned by Wales, but is generally accepted.

Since Sanger's departure from Wikipedia, he has been critical of the project, describing it in 2007 as being "broken beyond repair". He has argued that, despite its merits, Wikipedia lacks credibility and accuracy due to a lack of respect for expertise and authority. Since 2020, he has also accused Wikipedia of having a left-wing and liberal ideological bias in its articles.

In 2006, Sanger founded Citizendium to compete with Wikipedia; in 2010, he stepped down as editor-in-chief, and in 2020, he left Citizendium entirely. In 2017, he joined Everipedia as chief information officer (CIO). He resigned in 2019, to establish the Knowledge Standards Foundation and the "encyclosphere". As of 2023^[update], Sanger was serving as the executive director of the Knowledge Standards Foundation.

Lawrence Mark Sanger was born in Bellevue, Washington, on July 16, 1968. His father Gerry was a marine biologist who studied seabirds and his mother raised the children. When he was seven years old, his family moved to Anchorage, Alaska, where he grew up. He was interested in philosophical topics at an early age and decided "to study philosophy and make it my life's work" at the age of 16.

In high school, he participated in debate, which Sanger says influenced his views on neutrality due to these debates exposing him to different issues and arguments from both sides:

And so I'd look up articles about those things, and I was always furious when I came across an article that failed to present one side fairly or at all. The worst instances were when [the author] would just come out and say what their position is. It just struck me as being really unfair.

Sanger graduated from high school in 1986 and attended Reed College, majoring in philosophy. In college he became interested in the Internet and its potential as a publishing outlet. Sanger set up a listserver as a medium for students and tutors to meet for tutoring and "to act as a forum for discussion of tutorials, tutorial methods, and the possibility and merits of a voluntary, free network of individual tutors and students finding each other via the Internet for education outside the traditional university setting". He started and moderated a libertarian philosophy discussion list, the Association for Systematic Philosophy. In 1994, Sanger wrote a manifesto for the discussion group: