There are few psychometrically sound measures of coping in adults. Widely used measures of coping have highly unstable sub-scale analyses, were developed on homogenous samples, and are outdated. The scarcity of empirically derived instruments is concerning given that coping skills are linked to a variety of positive and negative physical and mental health outcomes (e.g., substance use, depression). Thus, the aim of the current study was to develop a psychometrically sound measure of coping in adults: the Adult Coping Inventory (ACI). The study consisted of three phases: The aim of Phase 1 was to generate an initial item pool. After eliminating redundant items, 124 items remained. The purpose of Phase 2 was to eliminate items based on item frequency and factor loadings. A diverse sample of 526 adults participated in the study. Following item generation and elimination, an exploratory factor analysis produced a 57-item, five-factor model of coping which included the following subscales: Problem Solving, Mindfulness, Maladaptive Coping, Social Support, and Avoidance. Overall, reliability of the ACI was excellent and the internal consistency of the factors ranged from adequate to excellent. Evidence of convergent, concurrent, and incremental validity of the questionnaire was also established. Results provide initial support for the psychometric properties of the ACI.