“…In the more than 40 years since the publication of Costello’s seminal article, research on low reward sensitivity and reward processing in depression has burgeoned, and reward or Behavioral Approach System (BAS; Gray, 1994) hyposensitivity is now one of the prominent models of major depression (Pizzagalli, 2014; Treadway & Zald, 2013). Similarly, the BAS or reward hypersensitivity model has become one of the leading biopsychosocial theories of the onset and course of bipolar spectrum disorders (BSDs; Alloy & Abramson, 2010; Alloy, Abramson, Urošević, Bender, & Wagner, 2009; Alloy, Nusslock, & Boland, 2015; Depue & Iacono, 1989; Johnson, 2005; Johnson, Edge, Holmes, & Carver, 2012; Urošević, Abramson, Harmon-Jones, & Alloy, 2008). Consequently, in homage to Costello’s recognition of the importance of the reward system in depression, in this article, we provide a model and up-to-date review of the role of reward sensitivity and processing in the onset and course of the full range of mood disorders--both unipolar depression and BSDs.…”