Infants acquiring their native language have to learn, among other things, the words of this language. To this end, they have to extract word forms from the continuous speech stream, therefore they need to segment it. In a first section, we will show that several low-level cues, directly accessible through a surface analysis of the speech signal, may allow young infants to find words in sentences even before the end of their first year of life. In addition, infants have to assign a meaning to these phonological forms. In the second section, we will see that this task may be facilitated by syntactic knowledge. Once again, we will investigate the role of cues that are directly available in the speech signal, function words and prosodic cues.