Abstract
Open Source Software (OSS) is a field of study with increasing interest of researchers. By its nature, OSS is especially suitable for empirical research. A great number of OSS related empirical studies have been conducted, but no effort has been made to systematically review the published evidence. This paper presents the results of a systematic review to investigate research topics and used methods in OSS related research. We present our results as facts and trends in this field and provide directions for future research.