Open source software (OSS) systems are being used for increasingly critical functions in modern societies, e.g., in health care, finance, government, defense, and other safety and security sensitive sectors. There is an increasing interest in software certification as a means to assure quality and dependability of such systems. However, the development processes and organizational structures of OSS projects can be substantially different from traditional closed-source projects. The distributed, “bazaar-style” approach to software development in OSS systems is often perceived incompatible with certification. This paper presents the results of a scoping review on certification in OSS systems in order to identify and categorize key issues and provide a comprehensive overview of the current evidence on this topic.