Whereas most existing differentiation measures are grounded in Bowen's writings about differentiation, the self-report instrument created in this study addresses differentiation according to the Four Points of Balance articulated by the Crucible Approach. The Crucible Differentiation Scale (CDS) is a 63-item, Likert-type, multidimensional measure of differentiation focused on adults and their important relationships. The psychometric properties of the CDS were tested through five studies with a total of 4,169 participants. The identified CDS subscales are Solid Self, Connectedness, Anxiety Regulation through Self-Soothing, Anxiety Regulation through Accommodation, Reactivity through Avoidance, Reactivity through Arguments, and Tolerating Discomfort for Growth. The CDS has potential use in evaluating differentiation theory, organizing treatment, and measuring therapy process and outcome.