In the present chapter, the most infuential theories of individuation of word meaning from both theoretical and computational linguistics are briefly reviewed, and then the psycholinguistic, as well as neurolinguistic, theories on lexical ambiguity are briefly presented. Finally, the linguistic and psycholinguistic theories are brought together in an attempt to reconcile these two fields and find a common domain of analysis. A distinction is made between words with multiple, 'unrelated meanings (i.e., homonymy) and words with multiple, related senses (i.e., polysemy). Psycholinguistic (as well as neurolinguistic) evidence in favour of this theoretical distinction is discussed, and the implications for the nature of the mental representations and the access system that may exist for the two types of ambiguous words are presented. (Ekaterini Klepousniotou)