The 250-odd photographs in this book had to run an arduous gantlet of editorial selection. For each one that was chosen for publication, thousands were examined, some never before seen in this century. Those that survived represent the work of 68 great photographers; hence, the title of this book.

What makes a photographer great? Not one great picture; hundreds of people, by design or accident, have achieved or stumbled upon an image that others consider great. Rather, inclusion in this collection signifies that a photographer accumulated a body of great work during his career.

In photography, as in any field, greatness is a quality more easily demonstrated than defined. Yet in researching this volume, the editors encountered several factors that, taken in combination, appeared to form a definition.

The first is intent. What did the photographer have in mind? When Alexander Gardner shows us an empty Civil War battlefield, he intends us to feel the sense of loss and tragedy he found there; when Lewis W. Hine poses a child beside an open door he intends us to ask, "Where does that door lead?" And when Yousuf Karsh shows us the broad brow of Nikita Khrushchev he intends that we feel the public power, wisdom and aggressiveness that are stored up behind it.

The second factor is skill. A great photographer must be able to execute his intention. He has to master all the tools at his command. He must exploit the qualities of light and film; must understand human nature, and know how to be patient at one moment, spontaneous at another. Without these skills even the noblest intent is unfilled.

Finally, the great photographer must execute his intention with a consistency lesser photographers cannot approach. The great photograph is no accident in the hands of these men and women. Whenever possible, the editors have looked at the whole life's work of each photographer represented here: with only a few exceptions, the early pictures and the late ones share the successful mark of their maker.

Intent, skill, consistency: however different the photographers in this book seem, they all share these qualities.