This dissertation examines Avicenna's theory of efficient causation in light of his approach to central problems in metaphysics, from the proof of the Necessary Existent to his emanative cosmology. Avicenna provides an internally coherent metaphysical account of efficient causation. A metaphysical account of the efficient cause explains the existence of the effect or essence in a way that is not explained by the causes of motion, as investigated in physics. That is, a full explanation of the cause of the existence (...) of an essence is not found in the four causes of natural change and motion. Avicenna aims to clarify what the explanatory division of labor is between the account of the natural philosopher and that of the metaphysician. In so doing, Avicenna develops a theory of causation that ties his innovative concepts of the contingent in itself and necessary in itself to the concept of efficient causation. A central distinction that Avicenna advances in relation to the efficient cause is that between the cause of the effect qua species and the cause of the effect qua individual. The distinction is relevant to understanding his view of the role of the causes of the essence, including the Active Intellect. Drawing on the above theory of efficient causation, the study reexamines Avicenna's famous proof for the Necessary Existent. The analysis shows that his metaphysical account of efficient causation is at the heart of his proof for a Necessary Existent. The "cause of persistence", in particular, is argued to have a more critical role than previously acknowledged, and is explicated in the context of his theory of efficient causation in metaphysics. (shrink)