This is an introduction to the grammar of words. Geert Booij introduces the basic methods of morphological analysis and shows how these can be used to reveal how words are formed, compounded, and inflected in different languages. He then describes the relationship of morphology to syntax, phonology, and semantics, and shows how the main aspects of grammar interact to make languages work. He ends by examining the universal characteristics of morphology. He discusses the ways in which these reflect the organization of the mind's language faculty and considers whether they throw light on the way languages change and are learned.