The importance of carotenoid cleavage reactions in plants and animals has been well-known since the early 1900s. These early studies demonstrated that ?-carotene was degraded to form Vitamin A, which is important for human health and plays a critical role in vision. However, the actual biochemical mechanisms involved, and the enzyme responsible for B-carotene cleavage in vivo, were not identified until the mid- to late-1990s (Wolf 1995; Woggon 2000, von Lintig and Vogt) (1-3). Also in the late 1990's, similar carotenoid cleavage enzymes were identified in plants and found to be important in the production of plant hormones (Schwartz et al., 1997) (4) and aroma compounds. These enzymatic cleavage reactions had only recently been discovered at the time of the last ACS symposium on Carotenoid Derived Aroma Compounds (Winterhalter and Rouseff, 2001) (5) and only three papers on enzymatic production of apo-carotenoids were presented. Since that time, the field has exploded and the importance of carotenoid cleavage enzymes in biological reactions has been well-established. The current ACS Symposium on Carotenoid Cleavage Products was designed to highlight these recent discoveries, focusing on the genetic and molecular biology of carotenoid cleavage enzymes, the importance of apo-carotenoids in flavor and aroma of fruits, vegetables, and wines, and the increasing interest in biotechnological aspects of apo-carotenoid production.These proceedings will be a valuable reference to food scientists, biochemists, and analytical chemists who are at the forefront of understanding the chemistry, analysis, and bioactivity of carotenoids and their cleavage products.