Leaves of Grass is a collection of poetry by American poet Walt Whitman, which was published originally in 1855. It has grown over time and many re-publications to contain over 400 poems, though the original edition only held 12. In Leaves of Grass, Whitman explores the idea of the "self" and how oneself is connected with the natural world. He expresses his thoughts on life's many mysteries, such as birth, life, death, and reincarnation. It is Whitman's life's work.