We aimed to define emotional infidelity among professional women who are in monogamous, cross-gender romantic relationships. We used constructivist grounded theory to capture participants’ lived experiences, perspectives, and worldviews. Eight currently partnered, self-identified women, established in their careers, and between the ages of 32 and 49, engaged in semi-structured initial, and brief follow-up, telephone interviews. Our data analysis and integration of participants’ perspectives and experiences revealed three main categories: (1) defining emotional infidelity, (2) how emotional infidelity occurs, and (3) relationship safeguarding. We developed a substantive, though preliminary, definition of emotional infidelity grounded in the literature and based on eight women’s discussion of emotional infidelity. Our hope is that researchers and practitioners would use this definition both as a model for investigating other population-specific definitions of emotional infidelity, and for better understanding and intervening upon relational processes related to emotional infidelity.