Parent report has proven a valid and cost-effective means of evaluating early child language. Norming datasets for these instruments, which provide the basis for standardized comparisons of individual children to a population, can also be used to derive norms for the acquisition of individual words in production and comprehension and also early gestures and symbolic actions. These lexical norms have a wide range of uses in basic research, assessment and intervention. In addition, cross-linguistic comparisons of lexical development are greatly facilitated by the availability of norms from diverse languages. This report describes the development of CLEX, a new web-based cross-linguistic database for lexical data from adaptations of the MacArthur-Bates Communicative Development Inventories. CLEX provides tools for a range of analyses within and across languages. It is designed to incorporate additional language datasets easily, and to permit users to define mappings between lexical items in pairs of languages for more specific cross-linguistic comparisons.