We are working towards defining a new class of Web-based Multi-Agent Systems (MAS) that can inherit the architectural properties of the Web (scalability, heterogeneity, evolvability, etc.), preserve the architectural properties of MAS (adaptability, openness, robustness, etc.), and are human-centric (usable, transparent, accountable, etc.). Our aim is to leverage the full potential of the Web as a middleware in MAS. In our approach, we consider the environment as a first-class abstraction in MAS – and we design the agents’ environment as a distributed hypermedia application guided by the design rationale of the Web architecture [1]. The distributed hypermedia environment provides agents with a uniform, knowledge-level abstraction of the system that they can navigate, query, observe, and act upon. The hypermedia-based design rationale reduces coupling and enhances the scalability, openness, and evolvability of the MAS. We refer to Web-based MAS that follow this design rationale as Hypermedia MAS.