Unpalatable food and unsatisfactory stand establishment are undesirable consequences of seed and grain deterioration. Considerable research has been generated in the last 15 years focusing on the physiology, repair, and assessment of seed deterioration, but this information has yet to be collated into a comprehensive review. The objective of this presentation is to systematically summarize these findings from a physiological perspective. A model of seed deterioration is forwarded arguing that free radical assault on mitochondrial membranes may be a primary cause of seed deterioration. The purpose of the presentation is to stimulate debate about the mechanism(s) of seed deterioration thereby improving our understanding and directing future study of this important event that compromises seed and grain quality.