|Abstract:||The subject matter of this study is the formal properties of infixes. This study begins with a catalogue of the placement properties of infixation in Chapter 1, showing that there is a bias for infixes to target edge constituents. This edge bias is explained in Chapter 4 in terms of the Exogenesis Theory of Infixation, which advocates the view that edge infixes originate from historical prefixes and suffixes; an infix’s original peripheral position is reflected in its edge profile today. A synchronic theory of infixation, Generalized Phonological Subcategorization (GPS), which allows non-prosodic units to enter into subcategorization relations, is proposed in Chapter 2 to encode the subcategorization requirement of an infix. Past theories of infixation are reviewed also in Chapter 2, with particular attention focused on the Hybrid Models which account for the prominence-driven infixes in terms of Prosodic Subcategorization while promoting Displacement Theory (DT) as a mean to explain the distribution of the edge-oriented infixes. Arguments on both theoretical and empirical grounds are summoned against DT’s view that edge infixes result from the movement of an underlying prefix or suffix acquiescing to certain phonological or morphological constraints. I advance the Subcategorization Non-violability Hypothesis, epitomized in the universal constraint ranking schema, M-ALIGN >> P, in Chapter 3 to supplement GPS by restricting the way morphological subcategorization requirement interacts with phonological constraints in the grammar; coerced affix movement (i.e. DT) is ruled out by virtue of the fact that constraints on morphological subcategorization must outrank all phonological constraints. Other typological aspects of infixation are reviewed in Chapter 5.