A new 2024 translation of Heidegger's Ph.D. Thesis on Duns Scotus. This edition contains a new afterword by the Translator, a timeline of Heidegger's life and works, a philosophic index of core Heideggerian concepts and a guide for terminology across 19th and 20th century Existentialists. This translation is designed for readability and accessibility to Heidegger's enigmatic and dense philosophy. Complex and specific philosophic terms are translated as literally as possible and academic footnotes have been removed to ensure easy reading. Martin Heidegger's dissertation on Duns Scotus, entitled "Duns Scotus' Doctrine of Categories and Meaning" (original German: "Die Kategorien- und Bedeutungslehre des Duns Scotus"), was originally submitted as a doctoral dissertation in 1915. Heidegger analyses Scotus's doctrine of categories and provides a detailed explanation of the Grammatica Speculativa, a work of medieval grammar now known to have been written by Thomas of Erfurt. This work is significant because it represents an early foray into Heidegger's lifelong philosophical concerns, particularly the question of being in the guise of the problem of categories and the question of language in the guise of the doctrine of meaning. Heidegger adopts a historical-philosophical approach, meticulously analysing and interpreting Duns Scotus' theories in the context of both medieval scholasticism and modern philosophical thought. He stresses the need to go beyond a purely historical analysis and to engage with the systematic philosophical content inherent in Scotus' work. Here Heidegger places a strong emphasis on categorisation, not just as an intellectual exercise, but as a critical tool for understanding the structure of reality and knowledge. The analysis delves into the nuances of Scotus' categories, exploring their implications for the conceptualisation of reality and the formation of meaning. This exploration is grounded in a clear understanding of the historical development of these ideas, providing a rich context for their appreciation and critique.