The worrying decline ofsocial capital (Putnam, 2000) and the disappointing trends of subjective well-being (Easterlin, 1974) raise urgent questions for modern societies: is the erosion of social capital a general feature of western societies or is it rather a characteristic aspect of the American one? Is there a relationship between the trends of social capital and subjective well-being? The available evidence suggests that two of the richest countries in the world, US and Great Britain, are following negative and considerably different trends of social capital and subjective well-being than other western societies. Present work provides further evidence focusing on Luxembourg. This country is characterized by peculiar economic and social conditions: it is the country with the highest GDP per capita in the world, more than 40% of its population is composed by immigrants and about 50% of its labor force is composed by cross-borders. All these elements raise strives and tensions which are common to many European countries making Luxembourg an interesting case of study. Main results of the present research are the following: 1. the erosion ofsocial capital is not a legacy of the richest countries in the world; 2. between 1999 and 2008, people in Luxembourg experienced a substantial increase in almost every proxy of social capital; 3. both endowments and trends of social capital and subjective well-being differ significantly within the population. Migrants participate less in social relationships and report lower levels of well-being; 4. the positive relationship between trends of subjective well-being and social capital found in previous literature is confirmed.