Michiel Baldur Maximiliaan van der Klis (born 9 June 1953) is a Dutch astronomer best known for his work on extreme 'pairings' of stars called X-ray binaries, more particularly his explanation of the occurrence of quasi-periodic oscillations (QPOs) in these systems and his co-discovery of the first millisecond X-ray pulsar. In the 1980s he gained worldwide fame with his investigation of QPOs. His revolutionary discoveries have had an enormous impact in his field of research; in effect, they have made it what it is today. Van der Klis pioneered special mathematical analysis techniques that are now regarded as the “gold standard” within his discipline.