Loneliness is gaining attention globally as a public health issue because elevated loneliness increases one's risk for depression, compromised immunity, chronic illness, and mortality. Our objective is to zoom into how loneliness has historically evolved through midlife and investigate whether elevations in loneliness are confined to the United States or are similarly transpiring across peer European nations. We use harmonized data on loneliness from nationally representative longitudinal panel surveys from the United States and 13 European nations to directly quantify similarities and differences in historical change of midlife loneliness trajectories. Compared with any other European nation/region, overall levels of loneliness in the United States are consistently higher by a magnitude of 0.3-0.8 SDs. Middle-aged adults in the United States, England, and Mediterranean Europe today report higher levels of loneliness than earlier born cohorts, whereas no historical changes (if not historically lower levels) were observed in Continental and Nordic Europe. Our discussion focuses on possible reasons for cross-national differences in midlife loneliness, including cultural factors, social and economic inequalities, and differences in social safety nets. (PsycInfo Database Record (c) 2024 APA, all rights reserved).