Every endeavour is covered by some fault, just as—re is covered by smoke. Therefore one should not give up the work born of his nature, even if such work is full of fault. – The Bhagvad-Gita (18.48) This book is the outcome of the research and developmentcontributions of partners from three different continents, Asia, Europe, America, coming from universities, research centers, industrial partners and SMEs (Small and Medium Enterprise), all of them collaborating in MAGNET (My Adaptive Personal Global Net) and MAGNET Beyond project supported by European Commission within the Sixth Framework Programme (FP6). The project was focusing on a secure user-centric approach developingsecure Personal Networks in multi-network,multi-device, and multi-user environments. The innovative concept of Personal Network (PN), which was introduced and developed in MAGNET, finds in this book the first confirmation of the success that the future of wireless communications is bound to achieve. The importance of this book is not only related to being the first work on PNs, it also gives an overview of operation of a big project, like MAGNET, and in fact the organisation of the book reffects how then project itself has been structured.