Natural cross-pollination has important implications in cotton breeding and cottonseed production. Control of the genetic complex that determines the potential value of a cotton plant for economic use is important, regardless of the breeding methods employed. In the past, natural crossing in cotton has received attention mainly as the cause of undesirable hybridization and mongrelization of seed stocks. Breeders have adopted artificial means of maintaining the genetic purity of their stocks, and allowable limits of segregation from other varieties have been set up for organizations engaged in the multiplication and distribution of cotton-planting seed. More recently, natural crossing in cotton has received increased attention because the phenomenon has possible use as a means of utilizing hybrid vigor and also for producing hybrid seed in commercial quantities. Formerly, studies were directed almost exclusively to reducing outcrossing; now, means of increasing natural crossing in cotton are of widespread interest.