A review is given of separation methods based on centrifugation. Attention is focused on separation of mixtures of gases and droplets. More particularly we consider: the method of gas centrifuges or ultra-centrifuges to separate gases of different molecular weight, and centrifugal separators to separate droplets from gases. Elementary physical principles are used to formulate basic equations. From here on, rules are derived for separation performance, energy consumption and size of the installations. Status of technology of each of the methods is illustrated by presenting actual cases of application.