<p>Repetitive negative thinking processes such as rumination and worry — also referred to as ‘perseverative thinking’ or ‘perseverative cognition’ — have traditionally been conceptualized as distinct processes defined, measured and studied in the clinical literature from a disorder-specific stance (for example, rumination in relation to depression, worry in relation to anxiety). However, rumination and worry are highly correlated, share phenomenological features, load onto a common factor, and predict and maintain multiple psychopathologies. In this Review, we overview the evidence base that conceptualizes repetitive negative thinking as an overarching cognitive process unconstrained by disorder-related content or temporal focus. The related theories and the empirical literature covering measurement, treatment and prevention support repetitive negative thinking as a transdiagnostic process. Adopting a transdiagnostic approach can help advance a more nuanced understanding of the role of repetitive negative thinking in clinical presentations and their treatment.</p>