While growing up in Cedar Rapids, Iowa, Milton Wright, the Wright brothers' father, likes to purchase toys for his sons that he hoped would stimulate their imagination. One of the most memorable gifts was a toy helicopter that was designed by the French aeronautical experimenter Alphonse Pénaud. Milton gave his sons this gift in 1878, and, though it was a simple device with a stick bound to a four-blade rotor set in a spindle, it had the intended effect-it caused them to dream. Twenty-five years separated the gift of this toy and their invention of the airplane, yet the Wright brothers were convinced it had exerted an important influence. Tom Crouch argued in The Bishop's Boys that toys like these perfectly illustrated the significance of play for technological innovation. He wrote, "rotary-wing toys were to intrigue and inspire generations of children, a few of whom would, as adults, attempt to realize the dream of flight for themselves." If the first powered flight on 17 December 1903 represented a childhood dream realized, it was only the first step in the rapid evolution of the airplane from their flimsy kite-like contraption of wood and cloth to jet airliners and rockets in space. And, as extraordinary as the achievement of powered flight seemed in 1903, before the end of the century, space travel also would become a dream realized. Soviet astronaut Yuri Gagarin first circumnavigated Earth in April 1961, and, eight years later, American astronauts took the first steps for humankind on the Moon.It is with great pleasure that we introduce Realizing the Dream: Biographical Essays in Honor of the Centennial of Flight. These essays in celebration of the Wright brothers' first flight 100 years ago grew out of presentations by a group of prominent scholars in 2003 at a conference sponsored by the NASA History Division and held at the Great Lakes Science Center in Cleveland, Ohio. The volume focuses on the careers of some of the many men and women who helped to realize the dream of flight both through the atmosphere and beyond. These accounts are original and compelling because they examine the history of flight through the lens of biography. Collectively, these individuals helped to shape American aerospace history. There are obviously many other individuals that could, and arguably should, have been included in this collection, but we believe that the cross section of diverse individuals contained in this volume is important because it is symbolic of the dream of flight as a whole. These people all devoted their lives, and sometimes even sacrificed them, to the demands required for its realization.