Callahan, North. Carl Sandburg: Lincoln of Our Literature. New York: New York University Press, 1970. A very readable biography of Sandburg, this volume contains excellent chapters on the Lincoln biographies.

Crowder, Richard. Carl Sandburg. New Haven: College and University Press, 1964. Although somewhat more difficult to read and less informative about the Lincoln books than Callahan's work, this study contains a good brief chronology of Sandburg's life and an annotated bibliography.