Since Paul and Zipf, it has become evident that lexical choice and meaning change are largely guided by pragmatic principles. Two central interacting principles are, first, the least-effort tendency to reduce expression and, second, the communicative requirements on sufficiency of information. Descendants of this opposition include Grice’s bipartite Maxim of Quantity (‘Make your contribution as informative as/no more informative than is required’) grounded within a general theory of rationality and cooperation, the Q and R Principles (essentially ‘Say enough’/‘Don’t say too much’), and the interplay of effort and effect within Relevance Theory. This chapter motivates a (Q-based) constraint on lexicalization, surveys the role of the R principle in motivating the Division of Pragmatic Labour, syntagmatic reduction, narrowing of meaning, euphemism, and negative strengthening, and provides pragmatic motivation for the lexical clone, un-noun, and un-verb constructions, and for the complementary Avoid Synonymy and Avoid Homonymy principles.