The study explores the prevalence, triggers, and psychological functions of nostalgia across 28 countries and Hong Kong, involving 2,606 young adults. Nostalgia, a bittersweet emotion tied to fond memories, is found to be common across cultures, though more valued in developed nations. It is triggered by psychological threats, sensory stimuli, and social gatherings, with effects varying by country. Induced nostalgia generally increases positive affect, though negative affect is mild. Recalling nostalgic memories enhances social connectedness, self-continuity, and meaning in life across cultures. In less-developed countries, ordinary memories also provide some of these benefits. Nostalgia also boosts life satisfaction in countries with lower living standards. The study confirms nostalgia's relevance across cultures and highlights cultural nuances in its functioning. Nostalgia is a complex emotion with social, self-related, and existential functions, serving as a psychological resource that helps restore well-being. It enhances social connectedness, self-esteem, and meaning in life, and buffers against psychological threats. The study also shows that nostalgia's effects vary by cultural orientation, with individualistic cultures valuing more personal triggers and collectivistic cultures emphasizing social ones. Additionally, nostalgia's buffering effect is stronger in countries with higher psychological threats. The findings suggest that nostalgia is a universal emotion with cultural variations in its expression and function.The study explores the prevalence, triggers, and psychological functions of nostalgia across 28 countries and Hong Kong, involving 2,606 young adults. Nostalgia, a bittersweet emotion tied to fond memories, is found to be common across cultures, though more valued in developed nations. It is triggered by psychological threats, sensory stimuli, and social gatherings, with effects varying by country. Induced nostalgia generally increases positive affect, though negative affect is mild. Recalling nostalgic memories enhances social connectedness, self-continuity, and meaning in life across cultures. In less-developed countries, ordinary memories also provide some of these benefits. Nostalgia also boosts life satisfaction in countries with lower living standards. The study confirms nostalgia's relevance across cultures and highlights cultural nuances in its functioning. Nostalgia is a complex emotion with social, self-related, and existential functions, serving as a psychological resource that helps restore well-being. It enhances social connectedness, self-esteem, and meaning in life, and buffers against psychological threats. The study also shows that nostalgia's effects vary by cultural orientation, with individualistic cultures valuing more personal triggers and collectivistic cultures emphasizing social ones. Additionally, nostalgia's buffering effect is stronger in countries with higher psychological threats. The findings suggest that nostalgia is a universal emotion with cultural variations in its expression and function.