Multilevel growth analysis was used to establish the shape of change (mean growth trajectory) for youth- and therapist-rated alliance in cognitive behavioral therapy (CBT) for anxious youth and to identify between-youth predictors of alliance trajectory. Youth (N = 69; ages 7-17; 52.2% female) and their parents participated in an empirically supported CBT protocol. Therapists rated alliance each session and youth every four sessions. Data were fit to four growth models: linear, quadratic, a dual slope, and a novel "alliance rupture" model. Two-level models were estimated to examine the effect of youth age, sex, pretreatment symptom severity, diagnostic comorbidity, early treatment factors (use of Selective Serotonin Reuptake Inhibitors), and coping styles (engagement, disengagement, and involuntary coping). A dual slope model fit therapist data best, whereas youth data did not evidence systematic growth. Two-level growth models identified that pretreatment anxiety severity predicted higher initial alliance levels. Depressive symptoms predicted less linear growth and engagement coping predicted greater growth during exposure sessions. No variables predicted preexposure growth. In the therapist model, 22% of initial alliance, 50% of preexposure growth, and 75% of postexposure growth were accounted for by between youth variables (mood disorder, anxiety and depression symptoms, engagement and involuntary coping). Therapist-reported alliance ratings may grow over the course of manual-based CBT, even during exposure-focused sessions. Pretreatment youth factors and coping style may influence the absolute value and linear trajectory of alliance during CBT. Findings about alliance-influencing factors can help set expectations for, and enhance training in, empirically supported treatments.