The founding document of the free software movement. richard-stallman posted an early version to net.unix-wizards in September 1983 (approximate date); the polished version appeared in Dr. Dobb's Journal in March 1985. Full coverage is in the Stallman KB — this entry focuses on the manifesto's role in the FOSS movement's history.
Role in the Movement
The GNU Manifesto established the ethical and programmatic foundation on which the entire subsequent movement rests. It announced the GNU Project and articulated why software must be free — not free of cost, but free for users to study, modify, and share. The philosophical framework Stallman developed here, later formalized as the four-freedoms, defined one pole of what would become the software-freedom-vs-open-source debate.
The manifesto was written before the legal mechanism of copyleft existed — that innovation came later with the gpl-v2 and its predecessors. But the manifesto articulated the goal that copyleft was designed to serve: ensuring that software freedom, once granted, could not be revoked. The hacker-culture-prehistory-1960s-1983 era it emerged from had seen proprietary software displace the sharing norms of the research community, and Stallman's response was to make those norms legally enforceable.
The GNU Manifesto's significance to the movement extends beyond its content. It represents the moment when a hacker culture norm — sharing source code — became an organized political project. Everything that followed, including the open-source-schism-and-dotcom-1998-2004, took place in its shadow. The "open source" movement of 1998 explicitly positioned itself as a less ideological successor to the free software tradition the manifesto launched — and eric-raymond's cathedral-and-the-bazaar-1997 is best understood as an answer to Stallman's question, with different values plugged in.
The manifesto was collected in free-software-free-society-2002, Stallman's essay collection. The free-software-foundation, founded by Stallman in 1985, was the institutional expression of the manifesto's program.