This booklet describes the Pioneer Program and its role in exploring the solar system. Sections include: (1) "Pioneers in Space to Understand Our Earth" (describing the background of the program); (2) "First Pioneers"; (3) "The Interplanetary Pioneers"; (4) "Planetary Pioneers"; (5) "Outer Solar System Pioneers"; (6) "The Pioneers Now and In the Future"; (7) "The Pioneer Spacecraft" (listing the launch date, mission, and status of 13 Pioneers); and (8) "Pioneer Firsts" (describing the first discovery and performance by the Pioneer Program). Many diagrams and photographs are provided. (YP)