Taking the unique perspective of Reinhart's Theta system (Reinhart 1991, 1996, 2000, 2002 et seq.) as its anchor, this book contributes to the understanding of the interface between the system of concepts and the computational system directly, and the inference systems, indirectly. The volume presents the Theta system, evaluates its merits and shortcomings, and introduces proposals for its refinement, from both a theoretical and an experimental perspective. The fact that it nurtures an active dialogue between the competing lexicalist and syntactic approaches on a broad array of lexico-semantic issues gives this book an extra dimension. The authors are not only researchers adhering to different frameworks, but also researchers working in different fields (be it semantics, syntax, morphology, or language acquisition). In empirical terms, the volume not only examines some of the notorious puzzles from a new theoretical perspective, but also brings new data and findings to light.