Callous-Unemotional (CU) traits identify children at high risk for antisocial behavior. Recent theoretical models propose that CU traits arise from low sensitivity to threat and affiliation. To assess these dimensions, we developed the parent- and self-reported Sensitivity to Threat and Affiliative Reward Scale (STARS) and tested its psychometric properties, factor structure, and construct validity. Samples 1 (N=303; age 3-10; US) and 2 (N=854 age 5-9; Spain) were children and Sample 3 was 514 young adults (Mage=19.89; US). In Sample 1, differential item functioning and item response theory techniques were used to identify the best-performing items from a 64-item pool, resulting in 28 items that functioned equivalently across age and gender. Factor analysis indicated acceptable fit for the theorized two-factor structure with separate threat and affiliation factors in all three samples, which showed predictive validity in relation to CU traits in children and psychopathic traits in young adults. **Keywords:** Affiliation; Callous-unemotional; Item Response Theory; Psychopathy; Threat **Authors:** Samantha Perlstein, Nicholas Wagner, Beatriz Domínguez-Álvarez, José Antonio Gómez-Fraguela, Estrella Romero, Laura Lopez-Romero, & Rebecca Waller Department of Psychology, University of Pennsylvania, Philadelphia, PA, USA Department of Psychological and Brain Science, Boston University, Boston, MA, USA Department of Clinical Psychology and Psychobiology, Universidade de Santiago de Compostela