Two variants of callous-unemotional (CU) traits and psychopathy have been proposed, referred to as primary and secondary . Whereas primary variants are thought to be underpinned by insufficient arousal to emotional cues, secondary variants are thought to develop as a coping mechanism in response to trauma exposure . Compared with adult samples, research on primary and secondary variants in children and adolescents under the age of 18 has only emerged in the past decade, and there is ongoing debate with regards to the identification, defining characteristics, and distinct correlates of these variants . The present systematic review synthesizes the current literature on primary and secondary variants in relation to: (1) constructs used to distinguish and define primary and secondary variants; (2) study population characteristics; (3) data analytic techniques to differentiate variants; and (4) differential associations with theoretically relevant indices related to emotional processing, maltreatment, biomarkers, and behavioral outcomes (e.g., substance use, aggression). This is the first systematic review to examine the growing literature on primary and secondary CU and psychopathy variants among youth . Findings support the distinction between youth with primary versus secondary variants and demonstrate that this distinction is related to unique clinical correlates . Recommendations are made for future research in the field.