Objective Relationship science has developed several theories to explain how and why people enter and maintain satisfying relationships. Less is known about why some people remain single, despite increasing rates of singlehood throughout the world. Using one of the most widely studied and robust theories—attachment theory—we aim to identify distinct sub-groups of singles and examine whether these sub-groups differ in their experience of singlehood and psychosocial outcomes. Method Across two studies of single adults (Ns = 482 and 400), we used latent profile analysis (LPA) to identify distinct sub-groups of singles. Results Both studies revealed four distinct profiles consistent with attachment theory: (1) secure; (2) anxious; (3) avoidant; and (4) fearful-avoidant. Furthermore, the four sub-groups of singles differed in theoretically distinct ways in their experience of singlehood and on indicators of psychosocial well-being. Conclusions These findings suggest that singles are a heterogeneous group of individuals that can be meaningfully differentiated based on individual differences in attachment security.