This chapter tackles the relation between declarative languages and multi-agent systems by following the dictates of the five Ws (and one H) that characterize investigations. The aim is to present this research field, which has a long-term tradition, and discuss about its future. The first question to answer is <em>"What? What are declarative agents and multi-agent systems?"</em>. Therefore, we will introduce the history of declarative agent systems up to the state of the art by answering the question <em>"When? When did research on them begin?"</em>. We will, then, move to the question <em>"Where? Where can it take place?"</em>: in which kind of real applications and for which kind of problems declarative agents and MAS have already proven useful? Connected to where is <em>"Why? Why should it happen?"</em>. We will discuss the benefits of adopting the abstractions offered by declarative approaches for developing communication, interaction, cooperation mechanisms. We will compare with other technologies, mainly service-based and object-oriented ones. <em>"Who? Who can be involved?"</em>: in order to exploit this kind of technology what sort of background does a specialist have to acquire? We address this question by looking at the Italian landscape of Computer Science research and education. Finally, with the question <em>"How? How can it happen?"</em> we will shortly report some examples of existing declarative languages and frameworks for the specification, verification, implementation and prototyping of agents and MAS.