Haploids have become one of the most effective tools in maize breeding. This chapter discusses two approaches utilizing maize haploids that have assumed great importance in commercial corn breeding. They are (1) producing and doubling the chromosomes in maternal haploids to generate double haploids (instant inbreds) and (2) utilizing paternal haploids produced utilizing the indeterminate gametophyte1 mutation to convert male-fertile lines into cytoplasmic male-sterile lines. Both approaches require only two generations, while traditional procedures require about seven to eight generations. These procedures have helped to make the breeding of corn more efficient and economical.