A modular valve system includes a number of functional components such as valves, pressure regulators, adaptors and manifolds for controlling a fluid flow through said valve system, and at least two connecting blocks of different configurations, each associated to one of said functional components. Each one of said connecting blocks constitutes a functional unit together with one functional component mounted on a functional side of said connecting block. All connecting blocks are formed in a rectangular block shape and have an inlet and an outlet on two opposing end sides constituting an inlet side and an outlet side, respectively. The inlet sides of all connecting blocks are of identical configuration. The outlet sides of all connecting blocks are also of identical configuration, wherein outlet and inlet of neighboring, coupled connecting blocks are aligned with each other. Therefore, functional units can be directly coupled for establishing a fluid flow.