In this paper, I propose a separate prosodic domain that regulates mora assignment in syllables: the Moraic Domain, a domain between the foot and the syllable in which only the head syllable may be moraic (see also van der Hulst & Moortgat 1980; LeSourd 1993; and Hermans & Torres-Tamarit 2014, among others, for other proposals of metrical domains between the foot and the syllable). I argue that this domain is necessary to account for the combination of two typological generalizations about vowel reduction. The first is the Ambiselectivity Generalization, according to which vowel reduction that decreases sonority (Crosswhite 1999; 2001; de Lacy 2002) may be restricted to foot-internal unstressed syllables, or to unfooted (minimal foot-external) syllables (see Martínez-Paricio 2013 for evidence). The second is the Sonority Requirement Generalization, which is derived from typological facts discovered by Crosswhite (1999; 2001); according to this generalization, a language may have at most one vowel reduction process that forces underlying low vowels to reduce to mid or high vowels. While accounts for each individual generalization may be derived from existing proposals without a Moraic Domain (Crosswhite 1999; 2001; Martínez-Paricio 2013), I show that no such account can derive both generalizations at once. In contrast, I argue that a Moraic Domain can account for both generalizations when embedded into Crosswhite’s (1999; 2001) account. This is demonstrated with a case study of Dutch semi-informal vowel reduction (Kager 1989), which cannot be derived in Crosswhite’s (1999; 2001) original approach without Moraic Domains.