The Communicative Development Inventories (CDIs) are parent report measures of vocabulary and other aspects of language development in very young children. They have evolved over the past 20 years to be one of the most well recognised assessments of infant language. Of particular significance is the fact that the CDIs are the first measures of their kind to be widely translated and adapted for use in many different languages. The inventories have served a variety of functions including measuring early language acquisition, deriving normative data on language acquisition, and both identifying and describing children whose early language is significantly delayed. This review describes the development of the CDIs, summarises the volume of research that has been generated in a range of applications of the measures, and evaluates their current standing both as a research tool and as a clinical measure. Issues around the sensitivity and predictive value of the CDIs are also considered.