Words are the building blocks of language. Native speakers typically know tens of thousands of words, which they combine into sentences to communicate an indefinite number of possible messages. A significant question in understanding how infants learn language is therefore to understand how they acquire words. This chapter focuses on two of the obstacles facing children learning words-first, how they discover which sequences of speech sounds cohere to form words (lexical segmentation), and second, how they learn to associate sound sequences with meanings (vocabulary acquisition). The connectionist simulations presented in this chapter provide a modelling framework for these two aspects of language acquisition. Although the simulations fall short of the scale and complexity of the learning task faced by infants, they provide an explicit account of some of the sources of information that are available to infants and how this information might be deployed in learning.