 Natural philosophy, or physics, in the strict sense is the study of natures; however, since by ‘nature’ most medieval natural philosophers meant an internal principle of change or motion that belongs to something essentially, natural philosophy came to be identified more specifically with the study of bodies insofar as they are subject of motion and consequently also with the conditions purportedly necessary for motion, such as the infinite, place, void and time. Within the medieval Arabic-speaking world there were two primary intellectual traditions in which natural philosophy was done: kalam and falsafa. Kalām, or Islamic speculative theology, in general approached issues in physics from an atomistic framework, which for some of these theologians extended not only to the composition of bodies, but also to motion and time as well, culminating among later Islamic theologians in an occasionalist worldview that reserved causal agency for God alone. Falsafa, or simply ‘philosophy,’ had its roots in the Greek intellectual world and more specifically in the philosophical thought of Aristotle as he was interpreted by later Peripatetic and Neoplatonic commentators with the additional supplementation by Galen in biology and anatomy and Ptolemy in astronomy. The following account begins with the atomistic theories found among the Islamic speculative theologians followed by the developments in Aristotelian natural philosophy by Arabic-speaking philosophers and their unique contributions to that field.