Critics consider The Petrified Forest to be Sherwood’s most successful play. It is about an intellectual war veteran facing a dangerous gangster in a diner out in the desert. It is available from the Dramatist’s Play Service.

Much of Sherwood’s information about Lincoln comes from the poet Carl Sandburg’s thorough biography, Lincoln: The Prairie Years, which is often bound with the other volume of his biography, The War Years.

Lincoln was very secretive about his family life. The source that most historians begin with for biographical information is the writings of William Herndon (who appears in the play as Billy Herndon). His biography is available as Herndon’s Life of Lincoln: The History and Personal Recollections of Abraham Lincoln. A 1997 collection called Herndon’s Informants: Letters, Interviews and Statements about Abraham Lincoln explores Herndon’s own sources of information.

One of the few book-length studies of Sherwood is John Mason Brown’s critical biography The Worlds of Robert E. Sherwood: Mirror to His Times, 1896–1939. Missing from this work is Sherwood’s career during World War II.

This play presents the formation of Lincoln’s sense of responsibility. The resultant sensibilities are examined in Mark E. Neely, Jr.’s 1992 Pulitzer Prize-winning study The Fate of Liberty: Abraham Lincoln and Civil Liberties.

Gore Vidal’s novel Lincoln is like Sherwood’s version in that it is an entertaining, speculative work, based in fact but stretched to tell an interesting story. It was reissued in a 1998 paperback edition.

Historians have long relied on Harvey Lee Ross’ book The Early Pioneers and Political Events of the State of Illinois, first published in 1899. It was reprinted in 1970 by Stevens Publishing Co. of Astoria, IL.