Since the first appearance of agents and multiagent systems (MAS), their close connection with declarative technologies was clearly devised and drove – and still drives – a large share of the research in the field. Declarative technologies play many roles in the MAS context: they can be exploited in the specification of the agents and MAS architecture, in the specification of their conversational flow, in their implementation, and in the representation of the agents’ knowledge. In all of these roles, one main advantage of declarative technologies is the support to transparency and explainability thanks to a (more, w.r.t. other paradigms) readable, understandable, and interoperable description of the system, and to reliability, by means of formal verification of its properties. This chapter, guided by works presented at Workshop on Objects and Agents (WOA) starting from 2000, discusses the crucial role that declarative technologies play in a MAS context.