Complex computational systems require new articulated abstractions for their modelling and engineering. This lecture will introduce the Agents & Artefacts (A&A) meta-model, by providing its conceptual, multi-disciplinary foundations, based on the notion of computational artefact as the tool that agents use to accomplish their own goals. A coherent definition of agent, artefact, and MAS is constructed, and related to the many definitions available in the literature, and some consequences in terms of models for MAS are drawn.