The past 20 years have witnessed an unparalleled surge in our knowledge about cognitive processes in obsessive-compulsive disorder (OCD). Innovations include identification of common thinking patterns in OCD, developing specialized cognitive therapy targeting specific subtypes, and, perhaps most significant, progress in understanding the origins of obsessions. The early behavioral focus was on preventing compulsive rituals and tolerating associated distress, but it is obsessional thinking that supposedly drives the neutralizing behaviors. Such thinking is no simple Cartesian matter as in "I think; therefore, I neutralize." Rather, I may think and therefore wash in the beginning, but, later, it may be I wash and therefore think I should wash more or feel I should wash and therefore think there must be a reason to wash or wash and forget why I thought I should. Obsessional thoughts are complex and multilayered. There are the thoughts that pop up, thoughts that hang around, thoughts about the thoughts I had and about the thoughts I didn't have or could have had. The person with OCD is caught in a cross current of such thoughts, where surface ripples turn into waves when they come up against a hidden bedrock of assumptions and beliefs. Early attempts characterized obsessions on the basis of their appearance; that is as unwanted aversive, alien intruders, distant from the values of the person and disturbing to their self-image (Rachman & Hodgson, 1980). For most clients, this is exactly how initial intrusive thoughts appear, and many subscribe to a fly-buzzing-around-the-head analogy and report metaphorically chasing the thought with a rolled up newspaper wishing aloud, "If only I could just get rid of this thought!" But of course, behavioral principles tell us that thinking like all behavior is actively, albeit often unwittingly, maintained by the person. The maintaining factors for obsessions are frequently appraisals. Appraisals give importance to the thoughts. Obsessional thoughts are upsetting, and sometimes they may grate against or exacerbate a personally perfectionist or overresponsible style of thinking or elicit unwelcome anxious reactions about future dangers or about the perceived uncontrollability or uncertainty of future events (see Clark, 2004; Frost, Novara, & Rheaume, 2002; Salkovskis, 1989; Wells, 2000). To the person experiencing intrusions, tormented as they are, it may seem prudent to keep the thoughts alive in order to understand them, in order to analyze them, in order to arrive at a solution. The thoughts, after all, may be telling me something about myself-about who I really am-otherwise why would they occur? The cognitive appraisal model formalized the relationship between initial intrusions and later appraisals applying Beck's model of psychopathology as a two-step process (Rachman, 1997; Salkovskis, 1989). In this model, the problem lies not with the initial intrusions but with their later evaluation and interpretation. These appraisals linked the intrusive content to wider pansituational beliefs that engender the distress and menace, reactions otherwise unwarranted by the content of the thought itself. Indeed, in this model, the content of initial intrusions is effectively normal, harmless, everyday, and ordinary and if left to go on its way would disappear like all similar thoughts after their 15 seconds of fame. This model provided the fertile ground for a most productive period in cognitive research that, through empirical, psychometric, and experimental studies, clearly demonstrated the power of appraisals and their clinical relevance and established their evaluation as a sine qua non for assessment procedures in OCD (Frost & Steketee, 2002). The appraisal model put cognitions on the map, but like all roads traveled, even if the signs pointing us in the right direction were clear initially, after a certain distance we are still wise to check our bearings. …