The examination of how words are learned can offer valuable insights into the nature of lexical representations. For example, a common assessment of novel word learning is based on its ability to interfere with other words; given that words are known to compete with each other, we can use the capacity of a novel word to interfere with the activation of other lexical representations as a measure of the degree to which it is integrated into the mental lexicon. This measure (...) allows us to assess novel word learning in L1 or L2, but also the degree to which representations from the two lexica interact with each other. Despite the somewhat independent lines of research on L1 and L2 word learning, common patterns emerge across the two literatures. In both cases, lexicalization appears to follow a similar trajectory. In L1, newly encoded words often fail at first to engage in competition with known words, but they do so later, after they have been better integrated into the mental lexicon. Similarly, L2 words generally have a facilitatory effect, which can, however, become inhibitory in the case of more robust lexical representations. Despite the similar pattern, L1 lexicalization is described in terms of inter-lexical connections, leading to more automatic processing ; whereas in L2 word learning, lack of lexical inhibition is attributed to less robust L2 lexical representations. Here, I point to these similarities and I use them to argue that a common mechanism may underlie similar patterns across the two literatures. (shrink)