Mobile devices are considered to be the next logical step in social networking as they become more pervasive and are able to establish direct communication with each other. Mobile social networking is a new movement in social networking as people have membership of both a virtual community through an online social network environment, and a physical community where they are located. A move in mobile social networking is the decentralised exploration of friendships. Short-range wireless protocols like Bluetooth enable collaborative applications between mobile devices of users. Unlike conventional centralised social networks that rely upon a central authority to organise the opinions of each member of the social network and protect their personal information, members of a decentralised network are completely autonomous and responsible for their own individual behaviour. When people meet for the first time, they thus need help to determine if they can trust each other. This book presents BlueTrust, a trust model for use in decentralised mobile social networks. BlueTrust focuses on establishing trust between users in close proximity by computing trust levels to support user interaction.