Chapter 13 describes models of confidence, focusing on tasks in which a confidence judgment is given after a primary decision. These judgments present difficulties for two-boundary decision models because they assume that the quality of the evidence at the time of the decision, expressed as a likelihood or posterior probability, will be constant and cannot provide a basis for confidence. The chapter analyzes the effect of drift-rate variability on the posterior probability and shows that it is not constant but decreases with time. It then considers four alternative models for postdecision response confidence. The first is the balance-of-evidence model of Vickers, in which evidence for competing responses is accumulated separately. The second is the postdecision accumulation model of Pleskac and Busemeyer. The third is the weighted evidence visibility model of Hellmann and colleagues, in which confidence depends on both the accumulated evidence and stimulus visibility. The fourth is an implementation of a related idea using a spherical diffusion model. The chapter briefly discusses the RTCON and RTCON2 models of simultaneous confidence of Ratcliff and colleagues, which are considered in detail in Volume 2.