City, University of London hosted the 13th International Conference on Compressors and their Systems on September 11 to 13, 2023, preceded by the sixth Short Course/Forum on computational fluid dynamics (CFD) in rotary positive-displacement (PD) machines, which took place on September 9 and 10. The 2023 edition was part of a series of biennial conferences starting in 1999 from a collaboration between City and the Fluid Machinery Group of the Institution of Mechanical Engineers (IMechE), which aimed to bring together researchers, academics, and professionals in the field of compressors and their systems from across the globe.