Leaves of Grass is a poetry collection by the American poet Walt Whitman (1819–1892). Although the first edition was published in 1855, Whitman spent most of his professional life writing and re-writing Leaves of Grass, revising it multiple times until his death. This resulted in vastly different editions over four decades—the first, a small book of twelve poems and the last, a compilation of over 400.The poems of Leaves of Grass are loosely connected, with each representing Whitman's celebration of his philosophy of life and humanity. This book is notable for its discussion of delight in sensual pleasures during a time when such candid displays were considered immoral.