Beck's insight-that beliefs about one's self, future, and environment shape behavior-transformed depression treatment. Yet environment beliefs remain relatively understudied. We introduce a set of environment beliefs-primal world beliefs or primals-that concern the world's overall character (e.g., the world is interesting, the world is dangerous). To create a measure, we systematically identified candidate primals (e.g., analyzing tweets, historical texts, etc.); conducted exploratory factor analysis (N = 930) and two confirmatory factor analyses (N = 524; N = 529); examined sequence effects (N = 219) and concurrent validity (N = 122); and conducted test-retests over 2 weeks (n = 122), 9 months (n = 134), and 19 months (n = 398). The resulting 99-item Primals Inventory (PI-99) measures 26 primals with three overarching beliefs-Safe, Enticing, and Alive (mean α = .93)-that typically explain ∼55% of the common variance. These beliefs were normally distributed; stable (2 weeks, 9 months, and 19 month test-retest results averaged .88, .75, and .77, respectively); strongly correlated with many personality and wellbeing variables (e.g., Safe and optimism, r = .61; Enticing and depression, r = -.52; Alive and meaning, r = .54); and explained more variance in life satisfaction, transcendent experience, trust, and gratitude than the BIG 5 (3%, 3%, 6%, and 12% more variance, respectively). In sum, the PI-99 showed strong psychometric characteristics, primals plausibly shape many personality and wellbeing variables, and a broad research effort examining these relationships is warranted. (PsycINFO Database Record (c) 2018 APA, all rights reserved).