A Coordianted Atomic Action (CA Action) is a unified scheme for coordinating complex concurrent activities and supporting error recovery between multiple interacting objects in distributed object-oriented systems. They constitute a very interesting concept for the structured developement of fault-tolerant distributed applications. To formalize the design of CA actions, this paper introduces a new language called COALA (COordinateed Atomic actions LAnguage). COALA provides both a concrete syntax to write CA actions and a semantics which formally explains the concept. The semantics is given in the formal object-oriented specification language CO-OPN/2. COALA can thus benefit form the formal techniques developed around CO-OPN/2 and use them for the validation and the test of applications written with COALA CA actions.