The book will introduce the reader into the field of secure communication for mobile application. Secure communications for mobile application covers, among others, secure web browsing with your phone (or PC), Single Sign On, mobile broadcast content protection, secure location services, etc. A new approach to application security has been recently standardized. This approach will be explained and the reasons and motivation that lead to its creation will be outlined. The benefits of the new system and its relationship to existing approaches will be given. The generic bootstrapping architecture of the mobile standardization body 3rd Generation Partnership Project (3GPP) and their American counterpart 3GPP2 will be outlined in full detail and with all variants. It offers the possibility to extend the cellular authentication to secure the communication for mobile applications and Internet services. 3GPP and 3GPP2 specified the core telecommunication standards, like GSM, GPRS, WCDMA and UMTS. The integration into existing networks and infrastructure is also, outlined and explained. Then the usage of the generic authentication architecture by various standardization bodies and standardized applications is described. This will cover mobile broadcast / multicast service security, Single-Sign-On, HTTPS (i.e. secure web browsing), secure data access, secure location services, etc. After this standardized use cases, some non-standardized ones are presented, like secure remote login to enterprise environment and card personalization. The intention is to cover two use cases in full detail and outline the other ones on a higher level. Tentatively, the Mobile TV / broadcast user case and the Single Sign On are most appropriate. A chapter on secure application implementation and integration will be provided. This chapter will allow application developers to integrate the solid security of the generic bootstrapping architecture into their web applications, streaming services etc. The relationship with Symbian Platform security will also be described. The book will close with the latest developments in the area of usage of the generic authentication architecture in fixed mobile convergence and Beyond 3G networks will be described e.g. usage for Mobile IP and policy access. This section will also cover the relationship between the generic authentication architecture and the IP Multimedia Subsystem (IMS) that is used for Voice over IP.