An electric propulsion unit (102) for an aircraft is shown. A fan (202) produces a pressured airflow (P) by raising the pressure of an incident airflow (I). An electric machine (201) is arranged to drive the fan and is located within a casing (204). A primary cooling circuit (205) is located within the casing, and includes the electric machine and a first pass of a fluid-fluid heat exchanger (208), thereby placing the electric machine and the fluid-fluid heat exchanger in thermal communication. A secondary cooling circuit includes a second pass of the fluid-fluid heat exchanger and an air-fluid heat exchanger (210) located within the pressurised airflow produced by the fan, thereby placing the fluid-fluid heat exchanger and the air-fluid heat exchanger in thermal communication.