The alliance is widely recognized as a robust predictor of posttreatment outcomes. However, there is a debate regarding whether the alliance is an epiphenomenon of intake characteristics and/or treatment processes occurring over the course of treatment. This meta-analysis aimed to synthesize the evidence on this issue. We identified 125 effect sizes in 60 independent samples (6,061 participants) of studies that reported allian-ceϪoutcome correlations as well as parallel intake or process characteristics. We examined the impact of these potential confounds on the allianceϪoutcome correlations. We meta-analyzed the studies estimates by computing omnibus effects models as well as multivariate models. We identified 3 variable types that were used to adjust the allianceϪoutcome correlations: (a) intake characteristics (k ϭ 35); (b) simultaneous processes, such as adherence or competence (k ϭ 13); and (c) both intake and simultaneous processes (k ϭ 24). We found moderate allianceϪoutcome correlations with or without adjustments for intake and simultaneous processes (range from r ϭ .23 to r ϭ .31). Our results provide robust empirical evidence for the assertion that the allianceϪoutcome association is an independent process-based factor. Findings suggest that alliance is positively related to outcome above and beyond the studied patient intake characteristics and treatment processes. Public Significance StatementThe alliance is a robust predictor of outcome at the between-patients level. Patients who report a stronger alliance during treatment are also likely to report better treatment outcome. This association remains significant when controlling for patients' intake characteristics and therapists' adherence and competence. These results demonstrate that the alliance is an independent process-based factor with unique contribution to outcome across many psychotherapeutic contexts.