Digital business transformation forces firms to develop foundational capabilities to remain competitive. However, despite considerable academic and managerial interest, the nature of a digital business capability (DBC) that creates value by effectively managing digital business transformation remains unclear. Drawing on a mixed-methods approach, we conceptualize and operationalize the DBC construct. In Study 1, we examine the effects of DBC on firm performance using a cross-industry, multisource dataset. In Study 2, we assess the effects of DBC on customer performance using a unique multisource, multilevel dataset collected at two points in time. The results reveal that DBC contributes to performance, even beyond the effects of established constructs. Importantly, DBC increasingly drives firm performance after reaching a critical level of internal dynamism (i.e., U-shaped moderation). By contrast, DBC particularly pays off at an optimal level of external dynamism (i.e., inverse U-shaped moderation). DBC is more valuable for business-to-consumer than for business-to-business firms.