This chapter provides an overview of conceptualizations of humor, the most prominent theories, and theories that may be a useful foundation for research on humor at work. Definitions of humor are manifold, ranging from a communicative activity with positive emotional reactions in perceivers to an individual trait (e.g., sense of humorSense of humor, cheerfulnessCheerfulness). Humor is seen as multidimensional construct and includes the abilities to produce, recognize, and appreciate humor and to use humor as a coping strategy. The three most prominent humor theories are the superiority, incongruity, and arousal-relief theories. We discuss the intra- and interpersonal functions of humor in general, the functions of humor at work, and humor measurement. Measures of (usually self-assessed) humor range from more trait-focused and internal perspectives to humor stylesHumor styles and humor in work contexts. A selection of 31 humor scales for work and general contexts is presented in Appendix.