Agent paradigm has been the subject of research for the last year, and the purpose of this book is to present the current status of this technology by looking at the applications in different domains, such as electronic markets, e-tourism, ambience intelligence, and analysis of complex systems. It begins by discussing the issues of software engineering for the development of multi-agent system, how much it costs to build a multi-agent systems, and the methods and tools currently available. Furthermore, this chapter some of the most relevant aspect to be considered for the development of multi-agent systems: ubiquitous computing, learning and planning, trust and security, electronic institutions and swarm intelligence.