The present book is a typological study in crucial portions of the grammars of French/Romance and German/Germanic. It starts by asking: What do adverbs, pronouns and full noun phrases have in common? This question is tackled, on the one hand, from an empirical perspective by the description of relevant linguistic facts leading to significant and unexpected generalizations, and, on the other hand, from a theoretical perspective by the formalization of (i) a novel model of the Xbar-schema containing at most two Specifiers (double Spec model) and (ii) a well-defined model of Checking Theory, distinguishing A-feature checking from Abar-feature checking (Criterion). The first part of the book deals with the typology and placement of adverbs, while the second part of the book presents the application of Checking Theory, in interaction with the double Spec model of Xbar-theory, to pronouns in Romance and Germanic. The final part of the book contains a treatment of scrambling in Germanic and shows that word order variations among arguments and adverbs within the German(ic) Mittelfeld can be adequately explained in the light of the version of Checking Theory and Phrase Structure Theory developed so far for adverbs and pronouns. We are led to the conclusion that the well-known issue of word order variations can find promising solutions with the Principles & Parameters framework, on the basis of a well-defined formalization of (i) Xbar-theory, (ii) Checking Theory, (iii) clause structure composition, and (iv) locality constraints on syntactic operations and relations.