In order to build their lexicon, infants firstly have to find word units in the speech stream, and then associate each word form with a meaning. This chapter discusses these two steps of lexical acquisition, and focuses more precisely on the role of two cues: phrasal prosody and function words. The main language-universal cue is the use of statistical or distributional information. The intuition behind the use of transitional probabilities between syllables or phonemes is that sound sequences that occur frequently and in a variety of contexts are better candidates for the lexicon than those that occur rarely or in few contexts. The syntactic category of words is the simplest cue that could constrain word meaning. Indeed, nouns typically refer to objects, whereas verbs generally refer to actions and adjectives to properties. Recent studies have demonstrated that young infants know something about the categories of function words.