There is clearly a need to optimize exposure therapy for youth, but at the same time very little empirical data exists regarding how exposure works or the best way to conduct exposures. Common wisdom about exposure, based on emotional processing theory, dictates that exposure works by breaking and eliminating conditioned fear responses through a process called habituation. This viewpoint dictates that exposure should be conducted until habituation occurs (i.e., until a physiological fear response reduces by at least 50%), and that habituation both during and between exposure sessions is necessary for improvement. As exposure therapy has evolved, other common practices have emerged that lack clear evidence supporting their efficacy. For example, it is common clinical practice to encourage youth to challenge their thoughts about a feared situation before and during an exposure (i.e., cognitive restructuring), even though clear evidence does not exist to support this practice. Additionally, it is common for clinicians to create a "fear ladder" or "hierarchy" with patients before beginning exposures. This hierarchy typically takes the form of a rank-ordered list of exposures or feared stimuli from least to most difficult, and clinicians move up this list systematically from the easiest to most difficult items during treatment. Again, there is little clear evidence to support this practice.