The Dark Factor of Personality (D) is the basic disposition that gives rise to specific personality traits related to antagonistic, malevolent, or socially aversive behavior, thereby representing the common core of dark personality traits. Whereas existing evidence clearly supports the conceptualization and utility of D, the assessment of D was possible only indirectly and with extensive effort, so far. Applying rational item selection techniques to seven large and highly heterogeneous samples (total N > 165,000), we herein identified sets of items (comprising 70, 35, and 16 items, respectively) that allow for a psychometrically sound and more concise assessment of D. Results indicate that all identified item sets are characterized by high internal consistencies and high retest-reliabilities, clearly map on a single factor in line with the definition of D, and exhibit substantial associations to various relevant criteria, including actual behavior. In particular, the item sets showed substantial associations with behavioral measures of individual utility maximization disregarding, accepting, or malevolently provoking disutility for others and were also related to various justifying beliefs, thereby mirroring the defining features of D. In sum, the identified item sets allow for a concise, reliable, and valid assessment of D. (PsycINFO Database Record (c) 2020 APA, all rights reserved).