The review article in this short book examines the nature, causes and consequences of affect at work. It focuses on two major categories of affect: moods and discrete emotions. The review is aimed at readers with an interest in affect and well-being at work, including researchers, practitioners, lecturers, and students of organizational and occupational psychology. Topics covered include: the nature of momentary affect; why it is important to study fluctuations in affect; major theories and methods that facilitate research on affect in the workplace; empirical evidence concerning the characteristics of the worker and work environment that cause mood; the consequences of mood for workers; the causes and consequences of discrete emotions at work (e.g., anger and envy); and future research challenges.