Merlyn Nielsen received a B.S. degree from the University of Nebraska (1970) and M.S. (1972) and Ph.D. (1974) degrees from Iowa State University. He was appointed assistant professor at the University of Nebraska in 1974, was promoted to associate professor in 1978 and professor in 1984. Merlyn is married to Elaine, and they have two children, Erin and Brian. Nielsen's early research developed procedures to predict breeding values in beef cattle. He wrote the computer programs used in the first national sire evaluations. In experiments with beef cows of similar mature size, he determined those cows with lower milk production were biologically and economically more efficient. Nielsen used carefully designed selection experiments in mice to evaluate an index of ovulation rate and prenatal survival, uterine capacity, or litter size as selection criteria. A model of ovulation rate and uterine capacity that mimicked co-variation between traits and responses in mice was developed, adding support to the use of this model in pigs. With selection for high and low heat production in mice as a proxy measure of energy for maintenance, Nielsen demonstrated that genetic variation for maintenance energy requirements exists, and thus similar genetic variation in livestock is expected. This novel research greatly advanced basic knowledge of genetic control of heat production, feed intake for maintenance, and associations with production traits in livestock. Merlyn Nielsen's research is innovative and productive, and he is an excellent collaborator. He has published over 60 refereed papers and has delivered invited papers at several international conferences. He served as section editor of Journal of Animal Science. He is an effective teacher and student advisor, having advised 13 M.S. and nine Ph.D. students.