The New York Hall of Science will develop a major exhibition on quantum theory--one of the most important developments in physical science in this century and one which has not been significantly treated by science museums. This exhibition will be the first major museum program to introduce quantum theory and its applications to the public. Elements of the exhibit will include models of the atom, the puzzle of light, applications of the theory and, finally, the human story of the creation of a new theory. Numerous participatory exhibits will be developed in conjunction with the project so that visitors can learn by doing. Formative evaluation will be an integral part of this exhibit. This technique has recently been adopted by museums as a way to test exhibit prototypes with museum visitors and then redesign as necessary. A workshop will be held for museum personnel and a guidebook, Improving Exhibits Through Formative Evaluation, will be produced. This book will be the first complete description of the formative evaluation process and will be a valuable addition to the museum field.