This work studies various aspects of word order and clause structure in Spanish that have proved problematic for syntactic theory. These aspects are explored theoretically in light of the antisymmetry approach of Kayne (1994) and empirically by examining parallel structures in related languages. For example, the author uses antisymmetry to critique the traditional understanding of post-verbal subjects, which have assumed a right-adjunction approach. However, he provides empirical as well as theoretical reasons to believe that a combination of leftward movements constitutes a better alternative. Likewise, the study uses a number of combined theoretical and empirical arguments to provide new and more constrained analyses of overt wh-movement and pre-verbal subjects. It shows that the obligatory post-verbal positioning of overt subjects cannot be explained by recourse to a required overt head movement of the verb. Instead, the author explains this restriction by proposing that overt subjects, which are always topicalized in Spanish, conflict with the feature specifications of wh-complementizers. Finally, the author relates the obligatory topicalized nature of pre-verbal subjects in Spanish to a proposal that person agreement morphemes on the verb should be considered arguments that receive the subject theta-role. This book will be of interest to syntacticians and comparitivists, as well as scholars of Romance languages.