The aspect of psycholinguistics that we will review in this chapter is to “explain on-line processing” as opposed to “time-free phonological knowledge”, which, we would claim, is the interest of theoretical linguistics (Hewlett, Gibbon, & Cohen-McKenzie, 1998: 161). Psycholinguists have usually attempted this through the description of models of speech production (and usually also perception). As Harley (2001) points out, speech production can be thought of as having three main stages: conceptualization (the message level), formulation (converting the message into a linguistic form involving word choice, syntax, and phonology/phonetics), and articulation (the motor execution of the formulation) (see also Levelt, 1989).