Just a decade ago, two psychologists, Swann, and Gómez, developed a new theoretical framework to explain extreme pro-group behaviors: identity fusion theory. Identity fusion refers to a visceral feeling of oneness with a group that motivates individuals to do extraordinary self-sacrifices on behalf of the group or each of its members. Since the formulation of the theory, interdisciplinary researchers of the five continents have conducted dozens of studies on identity fusion, both in laboratory and field settings. Research has deepened into the causes, consequences, underlying mechanisms, and applications of identity fusion. The development of fusion-based research has been steadfast and very prolific. Hence, the first section of the current manuscript includes an updated overview of this fast growing literature. This increasing interest for the theory has, however, been accompanied by a series of misconceptions and untested research assumptions, which we address in the second and third sections of the paper, concluding with a final section suggesting a future research agenda. Our aim is to help those interested in knowing more about identity fusion or about the causal mechanisms that lead individuals to risk their life and personal well-being for a group discarding common misconceptions as well as formulating more precise and nuanced hypotheses for future research.