Increasing attention is being paid to loneliness, and to its impact on the health of older people, across numerous disciplines including psychology, public health, social policy, and psychiatry. In tandem, there has been increasing interest in the impact of social factors on health. However, definitions of loneliness are disparate, and a consensus on its meaning is arguably lacking. Often, loneliness is conflated with similar but distinct concepts such as social isolation, absence of social support, or a lack of social connectedness. We submit that the concept of loneliness requires clarification, especially in the extant health literature. We attempt to synthesize theories of loneliness provide a framework for future interventions. We further argue that the necessary clarification can be achieved using both empirical and nonempirical methodologies, under a transdisciplinary effort. We describe the potential for psychology, public health, and philosophy to come together to achieve this conceptual clarity around loneliness and to develop effective interventions on this problematic experience as a result.