Developmental disorders offer a rare view into properties of language that might go unnoticed in typically developing individuals. Quite often such cases are used to demonstrate dissociations between language and the rest of cognition. Yet, detailed recent research suggests that the picture is more complex and nuanced. For instance, in high-functioning autism, we find a dissociation between vocabulary skills and the acquisition and processing of figurative expressions, suggesting that bigger-size lexical units (such as non-transparent idioms or conventional metaphors) are probably stored and processed differently than word-size items. Other populations, such as children with language impairment, have problems with units of a smaller size, namely morphemes, and how they are used to indicate relations of agreement in grammar. Children suffering from dyslexia experience problems in cracking the orthographic code and how it maps onto the sound structure of oral language. Finally, some children will only experience problems in understanding text and what individual words in a given text mean, but not in decoding itself. This chapter provides an overview of developmental deficits that affect language, with a focus on how lexical items are acquired, stored and processed in atypical populations.