This document discusses open source software (OSS) and its relevance to libraries and information professionals. It provides background on OSS, noting that it allows free access to source code and collaborative development. The document outlines how OSS principles align with libraries' goals of open access to information. It then gives examples of popular OSS used in libraries and digital libraries, including operating systems, library automation software, and digital library platforms. Finally, it argues that information professionals should actively participate in the OSS movement to develop shared resources and a gift culture of information exchange.