Process Algebra

The department of mathematics which investigates the relations and properties of numbers by means of general symbols; and, in a more abstract sense, a calculus of symbols combining according to certain defined laws. [Oxford English Dictionary]
Something going on [Webster]
Process algebra
An algebraic approach to the study of concurrent processes. Its tools are algebraical languages for the specification of processes and the formulation of statements about them, together with calculi for the verification of these statements. [Van Glabbeek, 1987]
The term "process algebra" was coined in 1982 by Bergstra & Klop [BK82]. A process algebra was a structure in the sense of universal algebra that satisfied a particular set of axioms. Since 1984 they used the phrase process algebra also to denote an area of science (i.e. as a noun without particle). In this meaning the phrase was sometimes used to refer to their own algebraic approach to the study of concurrent processes [BK86b], and sometimes to such algebraic approaches in general [BK86c]. The former use still occurs in [BW90] and [He88] for instance, but the latter, to which I also subscribe, is more widespread now.

The main algebraic approaches to concurrency are

The most popular books on process algebra are:

Applications of the ACP approach are collected in: A compact presentation of the foundations of the CCS approach is: Finally, a short paper reviewing and comparing CCS and CSP is For the historical references [Mi80, BHR84, BK82-84ab-85-86bc] see [BW90].
Rob van Glabbeek