An examination of emotions reported on 12 million personal blogs along with a series of surveys and laboratory experiments show that the meaning of happiness is not fixed; instead, it systematically shifts over the course of ones lifetime. Whereas younger people are more likely to associate happiness with excitement, as they get older, they become more likely to associate happiness with peacefulness. This change appears to be driven by a redirection of attention from the future to the present as people age. The dynamics of happiness has implications from purchasing behavior to ways to increase ones happiness.