This thesis presents an investigation of the three prominent models of language production: Levelt, Roelofs and Meyers (1999) two-stage account; Dell’s (1986) interactive account; and Caramazza’s (1997) Independent Network model. In particular, the thesis investigates four questions. First, is the activation of semantic, syntactic, and phonological representations serial or parallel? Secondly, is the flow of activation strictly modular, or is it cascading? Thirdly, how does the production system deal with the lemma level/syntactic representation of entries that whilst fixed, are larger than single words, e.g., idioms and fixed expressions? Finally, at what time point does the activation of syntactic information occur? Chapter 2 presents a tip-of-the-tongue (TOT) experiment in which support for cascading activation is found. Chapter 3 continues the use of the TOT paradigm to investigate the representation and a homophone advantage suggestive of shared phonological representations was found. Chapter 4 extends the TOT paradigm to the investigation of idiomatic expressions and the results suggest that both the literal and figurative meanings of an idiom are active during production – a finding that is best explained through bi-directional spreading activation. Chapter 5 continues the investigation of idiomatic expressions through a norming study and the results indicate that both native and non-native speakers can make fine-grained distinctions regarding idioms, but that this is heavily influenced by familiarity. Chapter 6 uses the picture-word interference paradigm to investigate the representation of count and mass nouns. The findings suggest that the activation of syntactic information is an early process and that mass nouns require the activation of an additional feature compared to count nouns. Finally, Chapter 8 presents the thesis conclusions, future directions for research, and argues that the evidence presented in the experimental chapters is strongly supportive of the interactive account of language production proposed by Dell (1986).