This volume contains the proceedings of CONCUR '93, the fourth in an annual series of conferences devoted to the study of concurrency. The basic aim of the CONCUR conferences is to communicate advances in concurrency theory and applications. The volume contains 31 papers selected from 113submissions, together with four invited papers and two abstracts of invited talks. The invited talks are: "The lambda-calculus with multiplicities" (extended abstract) by G rard Boudol, "A pi-calculus semantics for an object-based design notation" by Cliff B. Jones, "Partial-order methods for temporal verification" by Pierre Wolper and Patrice Godefroid, "Non-interleaving process algebra" by Jos C.M. Baetenand Jan A. Bergstra, "Loop parallelization in the polytope model" by Christian Lengauer, and "Structured operational semantics for process algebras and equational axiom systems" (abstract) by Bard Bloom.