Software that could be freely edited existed long before proprietary programs became the norm — but then it largely disappeared. When source-available, “free and open software” (FOSS) reemerged in the marketplace, it did so in a manner that was novel from both a social as well as a legal perspective. Today, it is an increasingly important part of the information technology landscape. In this article, I provide an overview of the history, legalities, social theory and commercial impact of the FOSS phenomenon, as well as some thoughts about its future.