It is often claimed that biology is autonomous from the physical sciences, but this is seldom made precise. This paper makes explicit, for the first time, five distinct ‘autonomy of biology’ theses. Three moderate theses concerning scientific status, methodological distinctness, and non-reducibility of biology to physics, are correct, and are nearly universally accepted. Two stronger theses concerning the exclusivity of biological explanation and irrelevance of physical laws, are shown to be false on the basis of two case studies of physical explanations of biological phenomena. Which scales and laws are explanatorily relevant for a particular phenomenon must be decided empirically.