Boost provides free peer-reviewed portable C++ source libraries. The emphasis is on libraries that work well with the C++ Standard Library. One goal is to establish "existing practice" and provide reference implementations so that the Boost libraries are suitable for eventual standardization. Some of the libraries have already been proposed for inclusion in the C++ Standards Committee's upcoming C++ Standard Library Technical Report.

Although Boost was begun by members of the C++ Standards Committee Library Working Group, membership has expanded to include thousands of members of the C++ community at large.