Precise natural language understanding requires adequate treatments both of single words and of larger units. However, expressions like idioms, verb-particle constructions and compound nouns may display idiomaticity, and while a police car is a car used by the police, a loan shark is not a fish that can be borrowed. Therefore it is important to identify which words in a sentence form an expression, and whether an expression is idiomatic, as this determines if it can be interpreted from a combination of the meanings of their component words or not. In this talk I discuss advances on the identification and treatment of multiword expressions in texts, focusing in particular on techniques for modelling idiomaticity.