The essay "On the Happy Life" was written around the year 58 AD destined to his older brother, Gallio, to whom Seneca also dedicated his dialogue De Ira ("On Anger"). Seneca explains that the search for happiness is the search for reason.

The main point to understand about the text is the title itself: 'Happy' here does not have the modern connotation of feeling good, but it is the equivalent of the Greek word eudaimonia, which is better understood as a life worthy of being lived, a state of plenitude of self. For Seneca and the stoics, the only life worth living is that of moral righteousness, the kind of existence we look at in the end and can honestly say that we are not ashamed. 

The depth of thought, the liveliness of style, and the rich examples provided by Seneca to confirm his theses make the reading of On the Happy Life extremely satisfying.