Prior meta-analyses have found a moderate but robust relationship between alliance and outcome across a broad spectrum of treatments, presenting concerns, contexts, and measurements. However, there continues to be a lively debate about the therapeutic role of the alliance, particularly in treatments that are tested using randomized clinical trial (RCT) designs. The purpose of this present study was to examine whether research design, type of treatment, or author's allegiance variables, alone or in combination, moderate the relationship between alliance and outcome. Multilevel longitudinal analysis was used to investigate the following moderators of the alliance-outcome correlation: (a) research design (RCT or other), (b) use of disorder-specific manuals, (c) specificity of outcomes, (d) cognitive and/or behavioral therapy (CBT) or other types of treatments, (e) researcher allegiance, and (f) time of alliance assessment. RCT, disorder-specific manual use, specificity of primary and secondary outcomes, and CBT did not moderate the alliance-outcome correlation. Early alliance-outcome correlations were slightly higher in studies conducted by investigators with specific interest in alliance than were those in studies conducted by researchers without such an allegiance. Over the course of therapy, these initial differences disappeared. Apart from this trend, none of the variables previously proposed as potential moderators or mediators of the alliance-outcome relation, alone or in combination, were found to have a mediating impact. (Contains 1 figure, 1 table, and 3 footnotes.)