Five studies document the validity of a new 8-item scale designed to measure positivity, defined as the tendency to view life and experiences with a positive outlook. In the first study (N = 372), the psychometric properties of Positivity Scale (P Scale) were examined in accordance with classical test theory using a large number of college participants. In Study 2, the unidimensionality of the P Scale was corroborated with confirmatory factor analysis in 2 independent samples (N₁ = 322; N₂ = 457). In Study 3, P Scale invariance across sexes and its relations with self-esteem, life satisfaction, optimism, positive negative affect, depression, and the Big Five provided further evidence of the internal and construct validity of the new measure in a large community sample (N = 3,589). In Study 4, test-retest reliability of the P Scale was found in a sample of college students (N = 262) who were readministered the scale after 5 weeks. In Study 5, measurement invariance and construct validity of P Scale were further supported across samples in different countries and cultures, including Italy (N = 689), the United States (N = 1,187), Japan (N = 281), and Spain (N = 302). Psychometric findings across diverse cultural context attest to the robustness of the P Scale and to positivity as a basic disposition.