After more than 20 years of empirical research, the resource-based view of the multibusiness firm has emerged as a promising paradigm for explaining diversification success—one of the most investigated research questions within the field of strategic management. However, because various dimensions of resource-relatedness, synergistic effects, and moderating influences are investigated at diverse levels of analysis, the findings are very fragmented. Our review and critical assessment of the research reveals a number of conceptual issues and methodological flaws that had already constrained heavily traditional diversification research. Consequently, we suggest promising directions for future research efforts that can put this important empirical application of the resource-based view of the firm on safer ground.