Privacy is of crucial importance in the era of global connectivity in which everything is inter-connected anytime and everywhere, with almost 2 billion world-wide users with connection to the Internet. Indeed, most of these users are concerned about their privacy. These concerns also apply for the new emerging research fields in computer science such as Multi-agent Systems. A Multi-agent System consists of a number of agents (which can be intelligent and/or autonomous) that interact with one-another. An agent usually encapsulates personal information describing its principal (names, preferences, tastes, credit card numbers, etc.). Moreover, agents carry out interactions on behalf of their principals. As a result, agents usually exchange personal information about their principals. This may have a direct impact on their principals' privacy. In this book, we focus on avoiding two information-related activities that can represent a serious threat for privacy in Multi-agent Systems: information collection and information processing.