The mechanical laws which make possible several characteristic and well-known modes of primate locomotion are reviewed. Biological requirements are fulfilled in small and in large primates by utilizing different mechanical principles. On the basis of the mechanics, special morphological traits can be identified which are advantageous for performing these locomotor modes, and which determine different lifestyles. These morphological ‘adaptations’ consequently are different in larger and smaller primates. The divergence between large and small forms is clarified by the inclusion of non-primate mammals into the comparis