The thesis claims that the linear organization of specifier, head and complement in a phrase and throughout a syntactic tree is determined by a conflict between general violable constraints on X-bar-structure. The adopted framework is Optimality Theory (cf. Prince & Smolensky 1993; in syntax, cf. Grimshaw 1997). The proposed constraint system explains why phrase structure directionality is mostly uniform and why only some non-uniform cases exist, while other logically possible kinds of mixed directionality are unattested. Central to the dissertation is the idea that head-initial oriented languages have a greater structural conflict to resolve inside their lexical projections than head-final languages: The combination of a general prefer...