Technical Abstract: Abundance of variation in maize was an important factor that made it a model system to study the principles of inheritance. Additional variation was subsequently created by mutagenesis. Most of these mutants have been donated to the Maize Genetics Cooperation ' Stock Center, where they have become a resource shared by the maize research community. Recent large-scale mutagenesis projects have developed resources that are being used to identify new mutants using forward and reverse genetics approaches. These mutants are giving us a basic understanding of maize biology and are useful resources in applied approaches to improve maize as a crop plant.