Romantic passion represents one of the most fragile and elusive elements of relationship quality but one that is increasingly valued and tied to relationship and individual well-being. We provide the first examination of whether experiencing personal self-expansion-positive self-change and personal growth without a romantic partner-is a critical predictor of passion. Previous research has almost exclusively examined the consequences of couples' sharing novel experiences (i.e., relational self-expansion) on romantic relationships. Instead, the consequences of personal self-expansion for romantic relationships remain largely unexamined even though most positive self-growth may occur without a romantic partner (e.g., at work). We investigated the consequences of personal self-expansion for passion in three studies including two 21-day experience sampling studies of community couples and a study in a context likely to elicit heightened personal self-expansion: during job relocation. Within-person increases in daily personal self-expansion were associated with greater passion through greater positive emotions (Studies 1 and 2). In contrast, high between-person levels of personal self-expansion were associated with lower passion through lower levels of intimacy, suggesting that individuals may drift apart from their partners with more chronic personal self-expansion (Studies 1, 2, and 3). That is, consistently growing outside of the relationship in ways that are not shared with a romantic partner may reduce feelings of closeness and connection, and ultimately passion. Results also suggest that chronic personal self-expansion may be a double-edged sword for individual well-being, simultaneously associated with lower passion, but greater fulfillment of competence needs. Results controlled for relational self-expansion and time together. (PsycInfo Database Record (c) 2021 APA, all rights reserved).