The origins of this book were in the cryptologic equivalent of an urban legend and a couple of photographs. During research on the early days of NSA, historians at the Center for Cryptologic History (CCH) learned of the employment of African-Americans at the Agency in the period after World War II. Occasionally, in informal conversations with former NSA seniors, the subject of minority history would come up, and CCH historians collected anecdotes about segregated offices in the early days. It became apparent that the employment of African-Americans came even earlier than previously thought. No information, however, confirmed any contribution by African-Americans during the world war. In early 1996, the History Center received as a donation a book of rather monotonous photographs of civilian employees at one of NSA's predecessors receiving citations for important contributions. Out of several hundred photographs, only two included African-Americans - an employee receiving an award from Colonel Preston Corderman (reproduced on page 14) and the same employee posing with his family. Although undated, the matrix of the photograph indicated it had been taken in 1945 or early 1946. This made it likely the person was receiving an award for wartime contributions. It therefore became a high priority in the History Center to investigate the story behind this photograph and learn the truth behind the unconnected anecdotes about African-Americans in the early days of the cryptologic organization. In 1998 it became possible to hire a few additional historians for a year to supplement the History Center's permanent staff. Ms. Jeannette Williams applied to research the early history of African-Americans in cryptology. Assisted by Ms. Yolande Dickerson, Ms. Williams undertook an exhaustive search of the cryptologic archives and recovered the basic story of the segregated cryptologic organizations - including the previously unknown existence of a large office of African-Americans in World War II. The basic facts about this unit preserved in official records, however, shed little light on the social milieu of the time or the eventual movement of African-Americans into the cryptologic mainstream. Compiling - and constantly expanding - a list of names of African-Americans who worked in the early days of NSA and its predecessor organizations, they conducted an exceedingly vigorous program of oral history interviews. These interviews personalized the stark facts found in the documents. In fact, this monograph rescues an important historical story that might otherwise have been lost. It should also be noted that this was a last-minute rescue. Several important figures had already passed away by the time the research for this book began, and several more have passed away between the time of their interviews and the publication of this book. The story that the author tells is by turns infuriating and inspiring. But it needs to be faced squarely from both these aspects. I recommend The Invisible Cryptologists: African-Americans, WWII to 1956 as essential reading for all who are interested in the early days of cryptology, all who are interested in the social history of NSA and its predecessors, and all who are interested in the history of American race relations. For further background on cryptologic activities during World War II and the early days of NSA, readers are encouraged to refer to A History of U.S. Communications Intelligence during World War II: Policy and Administration by Robert L. Benson and The Origins of the National Security Agency by Thomas L. Burns (forthcoming).