The BSD licenses are a family of short permissive licenses that originated with the Berkeley Software Distribution, the version of Unix developed by the Computer Systems Research Group at the University of California, Berkeley. Like the MIT License, they grant broad rights to use, modify, and redistribute software, in both source and binary form, provided that the copyright notice, the list of conditions, and the warranty disclaimer are preserved.
The most widely used variant is the 3-clause BSD License, which the Open Source Initiative also lists as the “New BSD License” or “Modified BSD License.” Its three conditions require that redistributions of source code “retain the above copyright notice, this list of conditions and the following disclaimer,” that binary redistributions “reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials,” and, in the third clause, that “Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.” That third clause is a non-endorsement provision, protecting the names of the original authors from being used in marketing.
The 2-clause variant, which the OSI lists as the “Simplified BSD License” or “FreeBSD License,” drops the non-endorsement clause entirely, leaving only the two redistribution conditions: source distributions must “retain the above copyright notice, this list of conditions and the following disclaimer,” and binary distributions must “reproduce the above copyright notice, this list of conditions and the disclaimer in the documentation.” The result is functionally close to the MIT License.
The family’s defining historical episode is the original four-clause form and its advertising clause. The earliest BSD license added a clause requiring that all advertising material mentioning features of the software display an acknowledgement crediting the University of California, Berkeley. As more BSD-derived code accumulated, this requirement compounded: a product built on dozens of independently licensed components had to list every contributor’s acknowledgement, an unworkable obligation. In 1999 the University of California formally retired the advertising clause from its own code, and the three-clause form became the standard, with the two-clause form following as an even simpler option.
The BSD licenses, alongside MIT, established the template for permissive open source licensing: minimal restrictions, no copyleft, and freedom to incorporate the code into proprietary products. Their Berkeley origin gave them deep roots in the Unix world, and BSD-licensed code from the CSRG era propagated into countless commercial and open systems, including parts of later operating systems that traced their networking stacks and utilities back to Berkeley.