Improvements to an HVAC thermostat include a sleep-enhancing feature which regulates the target temperature of the HVAC system according to a temperature profile which complements the natural changes in body temperature of a person during sleep. The timing of the temperature profile is advanced to cause room temperature to decrease before the natural decrease in body temperature is expected to occur, thereby helping lead a person into sleep without the use of pharmaceuticals or other artificial sleeping aids. The temperature profile causes room temperature to increase towards the end of the sleep period, thus avoiding disruptions of sleep when body temperature is lowest or during REM stages of sleep when the human body's ability to thermo-regulate is diminished. The rate of change of the target environment temperature is controlled to further enhance the quality and duration of sleep.