This ebook attempts to advance our understanding regarding HWI, and includes five contributions, among them four empirical and one theoretical. The first paper presents an investigation of the three most commonly used workaholism measures—the Workaholism Battery (WorkBAT), the Work Addiction Risk Test (WART) and the Dutch Work Addiction Scale (DUWAS)—in terms of their cross-validation, their temporal stability and their factor structure. The second, third, and forth papers compare between positive and negative predictors and subtypes of dispositional HWI. In the fifth paper, the authors apply a bio-psycho-social model to develop an integrated typology of HWI. Research on HWI is still in its infancy, and the present collection constitutes a fresh and promising step in the understanding of HWI.