This document discusses the growing mobile applications economy. It notes that more people access Facebook from mobile than desktop, and in 2009 there were over 3.7 billion mobile subscriptions globally. Mobile app usage is increasing rapidly in categories like social networking, news, sports and banking. The major mobile platforms like Symbian, Apple, Microsoft and Android are driving the app economy. Native, web and hybrid mobile apps are described and examples given. Challenges like platform fragmentation, billing and regulations are also discussed.