Nicolay and John Hay, who had worked alongside Nicolay as assistant secretary to Lincoln, collaborated on . It appeared in "The Century Magazine" serially from 1886 to 1890 and was then issued (1890–94) in book form as ten volumes, together with the two-volume "Complete Works of Abraham Lincoln". The resulting biography is a definitive resource on Lincoln and his times. Nicolay and Hay also edited Lincoln's "Works" in twelve volumes (1905). Finally, "Personal Traits of Abraham Lincoln" was published by Helen Nicolay in 1912.