Diachronic morphosyntacticians of all theoretical persuasions agree that there is a tendency for "more lexical" linguistic material to develop "more functional" characteristics over time, a process generally known as grammaticalization. While most previous work on grammaticalization has been conducted in surface-oriented functionalist frameworks, this dissertation aims to illuminate the deeper structural properties of a sub-set of these phenomena, diachronic affixation, as well as its much rarer opposite, de-affixation, a phenomenon in which previously bound material becomes a syntactically independent form. This approach differs from previous generative approaches to this problem in utilising a non-lexicalist, piece-based, syntactic approach to morphology, Distributed Morphology (DM), according to which both words and phrases are built by the same generative system. Besides providing a schematic typology for the structural properties of affix-genesis and highlighting the theoretical advantage of DM, this dissertation has four main theoretical points. First, it makes explicit predictions about the locus of newly affixed material. Second, it argues, that affix-exodus is no less natural a change than affix-genesis. Third, it explores the similarities between affix-exodus and two other varieties of linguistic change: morphological re-cuttings and the disintegration of complex heads. Finally, it demonstrates that similar phenomena can also occur within a word. This is predicted by a theoretical framework with the properties of DM specified above. In addition to its specific contribution to work on diachronic morphosyntax, this dissertation has implications for morphology, morphosyntax, and historical linguistics more broadly, and argues that no additional diachronic-specific component is needed in the grammar.