The MacArthur-Bates Communicative Development Inventories (CDIs), Third Edition and the corresponding Spanish-language Inventarios, are some of the most widely used and recommended measures of language and communication for young children. Used in both research and clinical settings, these parent report instruments help SLPs and other professionals screen children, develop a prognosis for children with language delays, plan effective intervention, monitor progress, and meet mandates for including parent input in child evaluation. The CDIs include measures for three age ranges: Words and Gestures form (ages 8 to 18 months). With this comprehensive instrument, parents document the child’s understanding of hundreds of early vocabulary items, and the form yields separate indexes of words understood and words produced. Then, parents record communicative and symbolic gestures the child has tried or completed; Words and Sentences form (ages 16 to 30 months). Parents use this comprehensive instrument to document the child’s production of hundreds of words, record the child’s use of early forms of grammar, and provide written examples of the child’s three longest utterances; CDI-III (ages 30 to 37 months). This shorter, single-sheet tool measures expressive vocabulary and grammar. The third edition of the CDIs includes updated norms, additional tools, and more administration formats and helpful resources. Each form is available in paper or electronic formats. (author abstract)