This new proceedings discusses developments in air, gas and refrigeration compressors, vacuum pumps, and expanders. It is the 13th edition of the International Conference on Compressors and their Systems, a three-day conference organised by the Centre for Compressors Technology at City, University of London in collaboration with, among other, the MEchE, IIR, and IOR. The conference offers a platform to identify current challenges in the field and provide the essential content and direction to shape future research. The International Conference on Compressors and their Systems series began in 1999 as a result of industrial consultation and a need for academic collaboration. Initially, the conference was organised by the Fluid Machinery Group of the Institution of Mechanical Engineers (IMechE) with the support of Holroyd. From 2009, the Centre for Compressor Technology at City, University of London took over its management and the conference is now one of the main conventions, taking place biennially in the UK, becoming world-renowned for its place in industry and academia to gather and discuss a broad range of topical issues related to compressors and compression systems. This year's conference has the theme "Compressors and Expanders in Future Energy Systems" and will be of interest to researchers and engineers in industry.