This chapter outlines the application of a cognitive behavioral protocol targeting intolerance of uncertainty (CBT-IU) for the treatment of GAD. The theoretical rationale and empirical support for the CBT-IU protocol are presented, followed by an overview of assessment and case conceptualization and a description of each treatment module. Intolerance of uncertainty is viewed as a higher-order cognitive process that drives the development and maintenance of the worry cycle in GAD. Negative beliefs about uncertainty and its consequences are posited to lower the tolerance threshold for the uncertainty in daily life situations, and lead to worry as an attempt to reduce uncertainty through mental planning and preparing. CBT-IU treatment components include (1) psychoeducation and worry awareness training, (2) reevaluation of the usefulness of worry, (3) reevaluation of negative beliefs about uncertainty, identification of safety behaviors, and belief testing through behavioral experiments, (4) problem-solving training and reorientation, (5) written exposure for hypothetical worries, and (6) relapse prevention planning. Each module can be flexibly applied according to a client’s particular presentation. The overarching goal of CBT-IU is to increase tolerance to uncertainty by developing more balanced beliefs about uncertainty and its consequences.