This paper gives an overview of the main streams of research on concurrency in declarative languages and motivates the definition of the new concurrent functional language EDEN. Proceeding from the premise that parallelism should be expressed explicitly we have equipped the language with an explicit representation of processes and process abstractions. It is based on a lazy functional language and offers dynamic creation of processes and communication channels and a safe treatment of nondeterminism. 1. Introduction and Terminology Today the majority of parallel programs is written in imperative languages. This programming paradigm forces the programmer to use low-level constructs for synchronization and interprocess communication and it offers no support for the verification of programs. In contrast to imperative languages, declarative languages have the advantage that programs are able to retain parallelism inherent in the problem specification. Functional and logic programs can be ...