The book approaches the conceptual background of Avicenna's account of efficient causality, outlining the positions held by him and his early interpreters (eleventh and twelfth centuries), as well as the arguments that support those positions. The first aim of the book is to show the systematic unity of the Avicennian doctrines on ontology and aetiology, highlighting the threads connecting the two. The second aim is to investigate Avicenna's influence over his interpreters, assessing continuities and discontinuities.