In this article, I present in a systematic way Aristotle’s understanding of movement (kinêsis) as efficient cause in the Generation of Animals. This aspect of movement is not disclosed in the approach to movement as an incomplete activity in contrast to energeia, which has been extensively discussed in the literature. I explain in which sense movement is the efficient cause of generation and how this movement is related to the other factors, in particular the source of movement, the seminal fluid, (...) pneuma, and the vital heat, as well as to the form and the soul. The role of movement as efficient cause of generation shows how, for Aristotle, form and soul are inseparable from matter and movement in nature. Explaining the role of movement as efficient cause of generation also helps to make sense of the multiplicity of factors involved in the efficient causality of generation. The key to articulating these factors with one another is the identity of form of the generative movement, which is specifically the same in the source, in the tools, and in the substance that is coming into being. (shrink)