A review of the main studies on the format of lexical representation in the initial stages of language development is presented. Current investigations reveal a significant level of phonological specificity in the representation of words in the first lexicon, even before age two years. These results can be explained from a theoretical framework that posits the existence of multiple levels of encoding and suggests differences in accessing the represented information as a function of task demands or vocabulary size. The existence of possible differences in the degree of specification of vowels and consonants represented in the lexicon is an area of current debate. This article discusses the present state of this debate in the light of recent findings from research with different languages, in populations with different linguistic environments (monolingual and bilingual) and from experimental approaches that involve varying degrees of cognitive demands.