Work serves important functions for the individual, such as generating income, structuring the day, forming identity, establishing and developing relationships as well as creating meaning. Thus work is essential and necessary for most people. Unsurprisingly, unemployment is related to several psychological and physiological problems. Despite the positive aspects of work, however, some seem to be driven by inner and outer forces to work in a compulsive and excessive manner. These are denoted as workaholics (Schaufeli, Taris, & Van Rhenen, 2008). As workaholism may have several severe health-related and social implications, as well have implications for working life, knowledge about this topic is of vital importance. This chapter addresses the following questions: What is workaholism? How can workaholism best be conceptualized? What are the psychometric qualities of particular workaholism instruments? Does workaholism differ from other already established constructs such as work engagement, passion for work, and work overinvolvement?