A thermostat for a climate control system includes an electronic memory in which at least three occupancy settings are stored. The occupancy settings including a pre-defined unoccupied temperature set-point associated with an unoccupied state, a pre-defined occupied temperature set-point associated with an occupied-awake state and a pre-defined sleep temperature set-point associated with an occupied-asleep state. The thermostat's microprocessor is configured to communicate with the memory, and to establish at least three time periods during the day. The microprocessor assigns to each time period one of at least three user-selectable occupancy states including an unoccupied state, an occupied-awake state and an occupied-asleep state. The microprocessor controls operation of the climate control system to maintain the unoccupied temperature set-point during any time period assigned the unoccupied state, the occupied temperature set-point during any time period assigned the occupied-awake state, and the sleep temperature set-point to any time period assigned the occupied-asleep state.