With the increasing integration of wireless short-range communication technologies in mobile devices, novel applications for spontaneous communication, interaction and collaboration are possible. In this book, we distinguish between active and passive collaboration. The devices help users become aware of each other and stimulate face-to-face conversation (active collaboration). Also, autonomous device communication for sharing information without user interaction is possible, i.e., devices pass information to other devices in their vicinity (passive collaboration). Spontaneous communication of mobile devices leads to so-called opportunistic networks, a new and promising evolution in mobile ad-hoc networking. They are formed by mobile devices which communicate with each other while users are in close proximity. This book investigates opportunistic networks in their entirety. The proposed concepts comprise system components, a node architecture, a system model and a simple one-hop communication paradigm for opportunistic network applications. One focus of this book is a profile-based data dissemination mechanism. Readers of this book would include graduate students and postgraduate researchers in both academia and industry, who wish to gain a deeper knowledge of opportunistic networks, its underlying idea and its potential capabilities.