This chapter offers general background for the analysis of ‘phonological word’ and ‘grammatical word’ in a cross-linguistic perspective. It outlines the defining characteristics of phonological word (including segmental and suprasegmental features and phonological processes), formulates restrictions on the length of a minimal word, and places ‘word’ within a hierarchy of phonological units. Defining features of grammatical word are outlined next. In most instances phonological words and grammatical words coincide. In some cases a grammatical word can consist of a number of phonological words, and vice versa. Typical instances of mismatches involve reduplication, compounding, and complex predicates, including serial verbs. Clitics—morphological units which form a phonological unit with a word preceding or following them—account for further mismatches. The reality of word and the nature of its orthographic representation are discussed next. The chapter concludes with an overview of the volume, and an appendix containing points to be addressed by fieldworkers.