This book constitutes the refereed proceedings of the Third International Conference on Coordination Models and Languages, COORDINATION '99, held in Amsterdam, The Netherlands, in April 1999. The 26 revised full papers presented were carefully selected from a total of 67 submissions. The book is devoted to the recently established class of models and languages variously termed coordination languages, configuration languages, architectural description languages, or agent-oriented programming languages. These formalisms provide a clean separation between individual software components and their interaction within the overall software organization and thus make complex applications more tractable, support global analysis, and enhance the reuse of software components.