Nearly 100 years ago, the philosopher and mathematician Bertrand Russell warned of the social dangers of widespread envy. One view of modern society is that it is systematically developing a set of institutions -- such as social media and new forms of advertising -- that make people feel inadequate and envious of others. If so, how might that be influencing the psychological health of our citizens? This paper reports the first large-scale longitudinal research into envy and its possible repercussions. The paper studies 18,000 randomly selected individuals over the years 2005, 2009, and 2013. Using measures of SF-36 mental health and psychological well-being, four main conclusions emerge. First, the young are especially susceptible. Levels of envy fall as people grow older. This longitudinal finding is consistent with a cross-sectional pattern noted recently by Nicole E. Henniger and Christine R. Harris, and with the theory of socioemotional regulation suggested by scholars such as Laura L. Carstensen. Second, using fixed-effects equations and prospective analysis, the analysis reveals that envy today is a powerful predictor of worse SF-36 mental health and well-being in the future. A change from the lowest to the highest level of envy, for example, is associated with a worsening of SF-36 mental health by approximately half a standard deviation (p < .001). Third, no evidence is found for the idea that envy acts as a useful motivator. Greater envy is associated with slower -- not higher -- growth of psychological well-being in the future. Nor is envy a predictor of later economic success. Fourth, the longitudinal decline of envy leaves unaltered a U-shaped age pattern of well-being from age 20 to age 70. These results are consistent with the idea that society should be concerned about institutions that stimulate large-scale envy.