A thermal management system comprises a first heat exchanger configured to exchange heat between a first component and a first working fluid, a first working fluid compressor downstream in first working fluid flow of the first heat exchanger and configured to compress the first working fluid, a second heat exchanger downstream in first working fluid flow of the compressor and configured to exchange heat between the first working fluid and a second working fluid and an expander downstream in first working fluid flow of the second heat exchanger, and configured to expand and cool first working fluid and deliver cooled first working fluid to the first heat exchanger. The system further comprises a third heat exchanger upstream in second working fluid flow of the second heat exchanger, and configured to exchange heat between a second component and the second working fluid.