Early vocabulary development is a reliable predictor of children's later language skills. The MacArthur-Bates Communicative Development Inventory (CDI) has provided a powerful tool to assess earlyvocabulary development in English and other languages. However, there have been no published CDI norms for Mandarin Chinese. Given the importance of large-scale comparative data sets for understanding the early childhood lexicon, we have developed an early vocabulary inventory for Mandarin. In this article, we report our efforts in developing this instrument, and discuss the data collected from 884 Chinese families in Beijing over a period of 12-30 months, based on our instrument. Chinese children's receptive and expressive lexicons as assessed by our inventory match well with those reported for English on the basis of CDI. In particular, our data indicate comprehension-production differences, individual differences in early comprehension and in later production, and different lexical development profiles among infants versus toddlers. We also make the checklists and norms of our inventory available to the research community via the Internet; they may be accessed from the Psychonomic Society's Archive of Norms, Stimuli, and Data, at www.psychonomic.org/archive.