A software patent is a patent that claims a monopoly on a method, process, or system implemented in software. Unlike copyright, which protects a particular expression of code, a patent can cover an underlying idea or technique, so that anyone who independently writes a program using that technique may infringe regardless of whether they ever saw the patented code. This independent-infringement property makes patents a structural danger to free and open source software: a project can be written entirely from scratch, distributed under a permissive or copyleft license, and still be sued for practicing a patented algorithm. Because free software is meant to be copied and modified by anyone, a patent that reads on a popular project threatens every downstream user at once.
The free software movement and many in the open source world treat software patents as fundamentally incompatible with software freedom. A license can grant the freedom to run, study, modify, and share a program, but if a third party - or even one of the program’s own contributors - holds a patent on a technique the program uses, that contributor or third party can still block users through the courts. Licenses therefore began incorporating explicit patent provisions, shifting from silence on patents to active defensive engineering inside the license text itself.
The Apache License 2.0 is one of the clearest examples. Its section 3, “Grant of Patent License,” has each contributor grant a “perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable” patent license to make, use, sell, import, and transfer the work, limited to the patent claims that their own contributions necessarily infringe. Crucially it pairs this with a patent retaliation clause: if a licensee initiates patent litigation alleging that the work or a contribution within it infringes a patent, then “any patent licenses granted to You under this License for that Work shall terminate as of the date such litigation is filed.” This converts the granted patent rights into a deterrent - sue over the software and you lose your own license to it.
The GNU General Public License version 3 took a similar but broader approach. As the Quick Guide to GPLv3 explains, GPLv3 includes an explicit patent license from every contributor and adds protection against patent deals that would benefit some users while leaving others exposed, so that a distributor cannot quietly secure patent peace for itself and not pass it downstream. The aim is to ensure that everyone who receives GPLv3 software receives the same patent safety, preventing a contributor from later turning around and asserting patents against the very community using their contribution. Together these provisions made patent grants a normal, expected part of major open source licenses written in the 2000s.
The deeper tension remains unresolved at the policy level. Patent offices in different jurisdictions disagree about whether and how software is patentable - the question of what constitutes patentable subject matter for computer-implemented inventions has been litigated and re-litigated for decades - and large companies amass patent portfolios partly as defensive deterrents against one another. License-level patent grants and retaliation clauses are a pragmatic response to a landscape the free software community would prefer did not exist at all. They do not abolish software patents; they domesticate them within the four corners of a license, trading a promise not to attack in exchange for the right to participate.