This paper presents an approach to modelling concurrent objects in the pi-calculus, in which the behaviour of a concurrent object is described by the composition of a process representing its functionality that allows maximum concurrency amongst method invocations, and a controller process constraining the permissible concurrency for the object. The ability to separately specify concurrent and functional behaviours will enable us to isolate and solve problems and difficulties involved with concurrency. The ?-calculus provides a reason foundation to analyse and identify the principle and properties of the separation and composition. For a particular form of controller, the normalised control process, the result of the composition is bisimilar to a process with the same pattern of control structure as the controller. Issues and examples for non- normalised control process are also discussed.Key-words: object models, p-calculus, concurrency constraints, concurrency controls, composition, synchronisation, concurrent objects, concurrency patterns