A modular valve system (10) to be mounted to a support, in particular a support in an electric control cabinet, comprises at least two individual valve modules (12) which can be fluidly connected to each other and to which at least one control valve unit (16) can be coupled in each case. The modular valve system (10) includes a process fluid section (90) comprising process fluid lines (78) through which a process fluid can flow, a control fluid section (32) comprising control fluid lines in at least some of the valve modules (12) through which a control fluid can flow, and a membrane (80) which is shared by at least some of the valve modules (12) and designed for controlling the process fluid in the process fluid section (90) while forming membrane valves (50) and for sealing off the control fluid section.