Reo is a domain-specific language for programming and analyzing coordination protocols that compose individual processes into full systems, broadly construed.Examples of classes of systems that can be composed with Reo include component-based systems, service-oriented systems, multithreading systems, biological systems, and cryptographic protocols.Reo has a graphical syntax in which every Reo program, called a connector or circuit, is a labeled directed hypergraph.Such a graph represents the data-flow among the processes in the system.Reo has formal semantics, which stand at the basis of its various formal verification techniques and compilation tools.