Modulating gas valves and systems for modulating gas flow to gas-fired appliances are disclosed. An illustrative modulating gas valve can include at least one main valve adapted to regulate the flow of gas through a main gas conduit, at least one regulator for regulating the gas pressure outputted by each main valve between a first gas pressure and a second gas pressure, and a modulator adapted to variably modulate the gas outputted by the gas valve at a pressure between the first and second gas pressures. The modulator can be used to modulate the main gas valve or valves between an infinite or discrete number of positions.