Peer-to-peer (P2P) has proven as a most successful way to produce large scale, reliable, and cost-effective applications, as illustrated for file sharing or VoIP. P2P storage is an emerging field of application which allows peers to collectively leverage their resources towards ensuring the reliability and availability of user data. Providing assurances in both domains requires not only ensuring the confidentiality and privacy of the data storage process, but also thwarting peer misbehaviour through the introduction of proper security and co-operation enforcement mechanisms. This book highlights how the continuous observation of peer behaviour and monitoring of the storage process is an important requirement to secure a storage system.