Goddard is a leading quantitative geneticist. He has made innovative contributions to quantitative and population genetics theory, in particular on the use of genetic markers in artificial selection programs in agriculture. A number of his methods have been adopted by livestock industries throughout the world. He developed a new multiple marker measure of linkage disequilibrium that allows the estimation of effective population size as a function of time in the past. He has developed statistical genetic methods to better understand the genetic architecture of complex traits, and has applied these to quantitative traits across a range of species.