Thought stopping (TS) has a long and established history as an effective mental control technique among the cognitive behavioural therapies (CBT). Recent claims have arisen, particularly from acceptance and mindfulness-based authors, that thought suppression--and therefore TS--is counterproductive. These claims take the syllogistic form: TS is a form of thought suppression. All thought suppression is counterproductive. Therefore TS is counterproductive. This paper examines the evidence for and against each of these propositions, covering the literature related to anxiety, depression, exposure therapy, and the special case of obsessive-compulsive disorder. It is concluded that TS is a very particular form of thought suppression. Undifferentiated thought suppression has mixed and mild effects on psychopathological mental states, but TS can be highly effective if it is applied judiciously within a CBT model. It can enhance a person's coping repertoire. And this effect appears to be stronger than any possible concurrent dilution of habituation effects in exposure therapy.