Avicenna was a prolific scholar and, throughout his career, authored eight complete summae of philosophy. Although these eight "main works" vary in terms of length, content, order, and intended readership, they all profess to contain a more or less "complete" version of Avicenna’s theoretical philosophy. So far, scholarship on Avicenna either selected only one or two of these "main works" as the primary target of investigation (leaving the others aside) or considered them mainly from the perspective of their apparent similarities with each other instead of using them for the purpose of identifying changes and modifications that could indicate a development in Avicenna’s thought. This volume, which contains the proceedings of the Third International Meeting of the "Avicenna Study Group" (Trier 2021), offers fourteen case studies – from all areas of philosophy – on the relationships between the eight summae to each other. Their common goal is to gain a better sense of both Avicenna’s intellectual development and his productivity as an author by taking a comparative look at several works at once. This volume seeks to encourage more studies that critically investigate the whole range of Avicenna’s "main works" and, thereby, to open-up a new avenue of research which will undoubtedly result in a more refined understanding of Avicenna’s philosophy.