In light of recent attempts to revive the operation of syntactic head movement and clitic movement in Phase Theory (Roberts 2010a, 2012), we argue that object clitics are underlyingly determiners in the syntax. Clitics engage in probe/goal relations to value and delete their uninterpretable Case features, and upon Agree, cliticize to their host via head-to-head incorporation. Although this account adopts the bare phrase structure theoretic mechanism employed by Ian Roberts to instantiate head movement (i.e., `defective goals'), the work outlined here diverges from the details of Roberts's account, most crucially by positing Abstract Case features on clitics. Based on clitic constructions from Standard Spanish, and various dialects, it will be demonstrated that the behavior of clitics, like that of other nominal elements, is governed by general abstract conditions on movement, namely Relativized Minimality (Rizzi 2013), Case Theory and the Phase Impenetrability Condition (Chomsky 2001, 2004, 2008). After a careful rethinking of well-known intervention and impenetrability effects (i.e., islands) involving clitics in Spanish, it is claimed that their movement, although unique in being both maximal and minimal, otherwise conforms to the standard conditions imposed on determiner phrases more generally. Contrary to recently influential Base Generation accounts, this work makes a case for distinguishing clitic movement from the movement of doubles, through a detailed study of Exceptional Case-Marking (ECM) constructions, where multiple clitic arguments can raise to object (Chomsky 2013). The complex array of possibilities involving clitic placement in these structures exemplifies the interaction of clitics with Case assignment and distinguishes the minimal nature of clitic head movement from XP movement of doubles. Finally, Chomsky's theory of Inheritance (2008) figures crucially in this account, as it is used to explain the order of clitics in clusters of two and three. Inheritance is also used to explain island effects that block clitic climbing. This study concludes by making the case that while in certain dialects, such as Los Angeles Vernacular Spanish (Parodi 2009a, 2011), clitics have apparently evolved into agreement/object markers, in most dialects, including the Standard, both direct object (DO) and indirect object (IO) clitics are argument pronouns that move to their derived positions in the syntax. Such pronominal clitics are contrasted with truly base-generated `morpheme' clitics, including `inherently' reflexive clitics and `speaker' ethical dative clitics (Strozer 1976), which cannot be doubled or related by the syntax to a corresponding stressed argument. The account that fellows then, although firmly within the movement tradition of clitics (Kayne 1975, Quicoli 1976) is intended to complement morphological approaches to clitic clustering with non-argument clitics (Cuervo 2013), and to shed light on the workings of the interface that relates the narrow syntax to the phonological component of the grammar.