Abstract: Open Source Software (OSS) is an emerging pattern in software development and IT strategy for many companies. Because OSS is based on giving away free software and making profits on services (e.g., customization and maintenance), there is an increasing interest in OSS and this is attracting many users and developers. Now companies across industries are adopting OSS as part of their main IT strategy because of the strategic benefits derived from using it. However, many non-IT employees, including executives and managers, do not have much knowledge about OSS, which often causes them confusion and difficulty in the matters of IT decision-making. Therefore, it is very important for organizations to understand what OSS is and what strategic benefits or challenges they must address while considering or adopting OSS as a part of their IT strategy. The goal of this paper is to review information on OSS and provide solid knowledge of OSS to developers and users. I seek answers to the following questions: (1) What is OSS? (2) Who are the developers and users? and (3) What are the developers` and users` benefits and challenges?