This volume formalizes, organizes and analyzes the relation of knowledge about language to decision-making in practice. It synthesizes research in psycholinguistics, educational linguistics and sociolinguistics, freely crossing subject fields to establish innovative and expert responses to some of the key debates in the field. Authored and compiled by leaders in their various specialties and collated and extensively re-edited from the award-winning Encyclopedia of Language and Linguistics 2nd edition, this collection will be an ideal one-stop desk reference solution for any linguistics professional and researcher interested in how language operates at the leading edge.