For more than two decades, private military and security companies (PMSCs) have become increasingly involved in armed conflicts. A common view is that PMSCs are menaces who simply take economic advantage of—and thereby aggravate—already bad situations. Yet, empirical research has rarely investigated these claims or the impact of commercial actors’ selling force-related services. This article investigates how PMSCs impact the severity of armed conflict in weak states and advances the argument that PMSC services increase the client’s military effectiveness. In turn, increased military effectiveness translates into increased conflict severity, the extent of which depends on type of service provided by the PMSC, the level of competition on the market, and oversight.