This book explores the interface between syntax and the other components of the grammar, particularly phonology, morphology, and argument structure. It contains case studies, on subjects such as clitics and complex predicates (auxiliary and modal verbs) in Romance and grounding theoretical analysis in constant exemplification. It shows that a careful analysis of their properties can lead to a better understanding of the interaction of the various components of the grammar. The syntactic properties of clitics are considered in relation to their phonological and morphological characteristic. The properties of auxiliary verbs are analysed from the perspective of the interface between argument structure and syntactic structure. Modal verbs are examined at the interface between syntax and phonology. The analyses of clitics and auxiliaries shed new light on the link between Romanian and Balkan/Slavic.