This article systematically reviews studies investigating the effect of three operationalizations of complexity in emotion experience (i.e., differentiation, covariation, and variability) on situational behavioral adaptation (i.e., physiological, cognitive, and overt action responses), and quantifies the results with meta-analyses. Twenty-seven studies of emotion complexity were identified and divided into four categories: (a) trait and (b) state studies within clinical samples, and (c) trait and (d) state studies within nonclinical samples. Most studies investigated trait emotion differentiation, revealing negligible to small effects (r range: .06 to .15). Only 4 studies in total assessed indicators of state emotion complexity. The theoretical assumptions behind the indicators of emotion complexity as well as the conceptualization of behavioral adaptiveness are critically discussed, and a number of future avenues for this type of research are proposed.