We will present two series of experiments investigating the early development of two abilities involved in lexical acquisition; word segmentation, and word representation. In the first series of experiments, we start exploring how 8- and 12-month-old French-learning infants segment fluent speech. Guided by the proposal that the emergence of segmentation abilities crucially depend on the rhythmic type of the language in acquisition, we test the proposal that the pattern of emergence in French will differ from that found for English (Jusczyk & Aslin, 1995; Jusczyk, Newsome & Houston, 1999), and will reflect the more central role of the syllable as a unit of segmentation in French. The second series of experiments explored the degree of phonetic detail that 20-month-old infants are able to use in the process of lexical acquisition (see also Stager & Werker, 1997; Werker et al., 2002). Two factors were explored more specifically: syllabic accentuation (first/unaccented vs. final/accented) and the nature of the contrasted phonemes (consonant vs. vowel).