Open source software is increasingly used for many types of mobile apps and wireless devices. A leading example is Funambol, the world’s most popular mobile open source server project. This chapter discusses the background of the Funambol project and how it applies to mobile learning in three specific areas: wireless device compatibility, data and content synchronization, and mobile device management. The chapter also discusses major trends that are affecting mobile open source software for mobile learning, challenges that are confronting mobile software developers and content authors, and the benefits of using open source software for mobile learning systems.