Of Leisure only survives in a fragmentary state. The work concerns the rational use of spare time, whereby one can still actively aid human kind by engaging in wider questions about nature and the universe.
The text begins mid-sentence, and ends rather abruptly. In the Codex Ambrosianus (the main source for Seneca's essays) it is simply tacked onto the end of De Vita Beata suggesting a scribe missed a page or two.
The addressee has been erased but appears to have been seven letters long and is assumed to have been Seneca's friend Serenus.

Seneca's Essays Series:

1. Of providence - addressed to Lucilius
2. On the Firmness of the Wise Man - addressed to Serenus
3.-5. Of Anger (Books 1-3) - addressed to his brother Novatus
6. Of Consolation - addressed to Marcia
7. Of a Happy Life - addressed to Gallio
8. Of Leisure - addressed to Serenus
9. Of Tranquillity of Mind - addressed to Serenus
10. On the Shortness of Life - addressed to Paulinus
11. Of Consolation - addressed to Polybius
12. Of Consolation - addressed to Helvia