This Fourth Edition of Principles of Seed Science and Technology, like the fIrst three editions, is written for the advanced undergraduate student or lay person who desires an introduction to the science and technology of seeds. The fIrst nine chapters present the seed as a biological system and cover its origin, development, composition, function (and sometimes nonfunction), performance and ultimate deterioration. The last nine chapters present the fundamentals of how seeds are produced, conditioned, evaluated and distributed in our modern agricultural society. Two new chapters have been added in this fourth edition, one on seed ecology and the second on seed drying. Finally, revisions have been made throughout to reflect changes that have occurred in the seed industry since publication of the Third Edition. Because of the fundamental importance of seeds to both agriculture and to all of society, we have taken great care to present the science and technology of seeds with the respect and feeling this study deserves. We hope that this feeling will be communicated to our readers. Furthermore, we have attempted to present information in a straight-forward, easy-ta-read manner that will be easily understood by students and lay persons alike. Special care has been taken to address both current state-of-the-art as well as future trends in seed technology.