John Hay believed that “real history is told in private letters,” and the more than 220 surviving letters and telegrams from his Civil War days prove that to be true, showing Abraham Lincoln in action: “The Tycoon is in fine whack. I have rarely seen him more serene & busy. He is managing this war, the draft, foreign relations, and planning a reconstruction of the Union, all at once. I never knew with what tyrannous authority he rules the Cabinet, till now. The most important things he decides & there is no cavil.”

Along with Hay’s personal correspondence, Burlingame includes his surviving official letters. Though lacking the “literary brilliance of [Hay’s] personal letters,” Burlingame explains, “they help flesh out the historical record.” Burlingame also includes some of the letters Hay composed for Lincoln’s signature, including the celebrated letter of condolence to the Widow Bixby.

More than an inside glimpse of the Civil War White House, Hay’s surviving correspondence provides a window on the world of nineteenth-century Washington, D.C.

On 18 April 1861, assistant presidential secretary John Hay recorded in his diary the report of several women that "some young Virginian long haired swaggering chivalrous of course. . . and half a dozen others including a daredevil guerrilla from Richmond named Ficklin would do a thing within forty eight hours that would ring through the world."

The women feared that the Virginian planned either to assassinate or to capture the president. Calling this a "harrowing communication," Hay continued his entry: "They went away and I went to the bedside of the Chief couché. I told him the yarn; he quietly grinned."

This is but one of the dramatic entries in Hay’s Civil War diary, presented here in a definitive edition by Michael Burlingame and John R. Turner Ettlinger. Justly deemed the most intimate record we will ever have of Abraham Lincoln in the White House, the Hay diary is, according to Burlingame and Ettlinger, "one of the richest deposits of high-grade ore for the smelters of Lincoln biographers and Civil War historians." While the Cabinet diaries of Salmon P. Chase, Edward Bates, and Gideon Welles also shed much light on Lincoln’s presidency, as does the diary of Senator Orville Hickman Browning, none of these diaries has the literary flair of Hay’s, which is, as Lincoln’s friend Horace White noted, as "breezy and sparkling as champagne." An aspiring poet, Hay recorded events in a scintillating style that the lawyer-politician diarists conspicuously lacked.

Burlingame and Ettlinger’s edition of the diary is the first to publish the complete text of all of Hay’s entries from 1861 through 1864. In 1939 Tyler Dennett published Lincoln and the Civil War in the Diaries and Letters of John Hay, which, as Civil War historian Allan Nevins observed, was "rather casually edited." This new edition is essential in part because Dennett omitted approximately 10 percent of Hay’s 1861–64 entries.