Modular irrigation controllers and related methods are described herein. In one implementation, an irrigation controller comprises a control unit within a housing, the control unit including a first microcontroller for executing stored irrigation programs. The controller also comprises a plurality of module coupling locations, each electrically coupled with the first microcontroller and adapted to receive one of a plurality of expansion modules. The first microcontroller is configured to detect the electrical coupling and decoupling of an expansion module to a respective module coupling location without removing power to the control unit, the expansion module including a second microcontroller capable of communicating with said first microcontroller and including driver circuitry for actuating irrigation valves, the second microcontroller capable of operating the driver circuitry for actuating said irrigation valves in accordance with control signals received from the first microcontroller.