Allen, Gay Wilson, The New Walt Whitman Handbook, New York University Press, 1975.

This useful reference guide to Whitman is the work of one of his most influential twentieth-century critics and biographers.

Beaver, Joseph, Walt Whitman: Poet of Science, King's Crown Press, 1951.

This study explores a number of scientific themes that relate to "When I Heard the Learn'd Astronomer."

Gay, William, Walt Whitman: His Relation to Science and Philosophy, Firth & M'Cutcheon, 1895.

Gay provides an early analysis of Whitman's contribution to scientific and philosophical fields.

Loving, Jerome, Walt Whitman: The Song of Himself, University of California Press, 1999.

Loving presents a thorough biography of Whitman.

Reynolds, David S., ed., A Historical Guide to Walt Whitman, Oxford University Press, 2000.

Reynolds places Whitman into the political, literary, and social context of his era with a collection of interdisciplinary essays.

Thomas, M. Wynn, The Lunar Light of Whitman's Poetry, Harvard University...