Deviant sexual fantasies have long been regarded as an important factor in sexual offending, with research showing that they serve multiple functions (e.g., inducing arousal, planning behavior) and interrelate with numerous other factors (e.g., emotional states, personality). However, within this chapter, an evaluation of the existing theoretical accounts is provded, which indicates that the construct is not well understood or conceptualized. As a result, the authors present a new model; The Dual-Process Model of Sexual Thinking (DPM-ST). This account is developed by drawing upon relevant research from socio-cognitive psychology and mental imagery and knitting it with existing research on deviant sexual fantasies. The DPM-ST states that associative processes are involved in the generation of intrusive sexual thoughts, whereas controlled processes are responsible for the deliberate, effortful, and goaloriented act of sexual fantasizing. Research supporting the model is outlined, as are various implications for future research and clinical practice.