This book was developed from the 3rd International Congress on MaleMediated Developmental Toxicity held at the University of Bradford from 31st July 2005 to 3rd August, 2005. The International Congresses on Male-Mediated Developmental Toxicity are held every 4–5 years and serve as a focal point for discussion of male germ line mutagenesis that can lead to developmental defects in the next generation.