After summarizing the contributed chapters, this concluding chapter briefly explores three societal developments not discussed in detail in the chapters: loneliness among older migrants as a structurally disadvantaged group, the growth of populist parties and their relation to loneliness, and the potential impact of increased artificial intelligence use on loneliness. We offer suggestions for future research directions to advance the study of macro-level influences on loneliness. We then proceed with a more rigorous evaluation of loneliness interventions. Next, we argue that a deeper understanding of how multi-level factors impact loneliness requires a closer examination of the cognitive approach to loneliness. This approach views loneliness as a mismatch between the quality and quantity of social relationships one has and what one desires. Each potential condition of loneliness can be evaluated based on its impact on the ideal and achieved quality and quantity of social relationships. If the achieved quality or quantity deteriorates, loneliness will occur unless the ideal quality or quantity is adjusted to restore balance. Different types of loneliness can result from various disturbances. We conclude with a brief discussion on how the book might have transformed our understanding of loneliness conceptually, theoretically, methodologically, and from a policy perspective.