The influence of phonological (i.e. individual sounds), lexical (i.e. whole-word forms) and semantic (i.e. meaning) characteristics on the words known by infants age 1;4 to 2;6 was examined, using an existing database (Dale & Fenson, 1996). For each noun, word frequency, two phonological (i.e. positional segment average, biphone average), two lexical (i.e. neighborhood density, word length) and four semantic variables (i.e. semantic set size, connectivity, probability resonance, resonance strength) were computed. Regression analyses showed that more infants knew (1) words composed of low-probability sounds and sound pairs, (2) shorter words with high neighborhood density, and (3) words that were semantically related to other words, both in terms of the number and strength of semantic connections. Moreover, the effect of phonological variables was constant across age, whereas the effect of lexical and semantic variables changed across age.