A general framework for the denotational treatment of concurrency is introduced. The key idea is the notion of process which is element of a domain obtained as solution of a domain equation in the style as considered previously by Plotkin. We use tools from metric topology as advocated by Nivat to solve this equation, show how operations upon processes can be defined conveniently, and illustrate the approach with the definition of a variety of concepts as encountered in the study of concurrency. Only few proofs of the supporting mathematical theory are given; full proofs will appear in the final version of the paper.