Mapping the Left Periphery , the fifth volume in "The Cartography of Syntactic Structures," is entirely devoted to the functional articulation of the so-called complementizer system, the highest part of sentence structure. The papers collected here identify, on the basis of substantial empirical evidence, new atoms of functional structure, which encode specific features that are typically expressed in the left periphery. The volume also submits the richly articulated CP structure to further crosslinguistic checking. The research presented here has led to the identification of new, important restrictions in the relative sequence of elements appearing in the left periphery.