Cytoplasmic male sterility is an important part of hybrid maize production. The first commercial cytoplasmic male sterile, discovered in Texas, is known as CMS-T. The use of CMS-T, starting in the 1950s, eliminated the need for detasseling. In the early 1970s, plants containing CMS-T genetics were susceptible to southern corn leaf blight and suffered from widespread loss of yield. Since then, CMS types C and S were used instead. Unfortunately, these lines are prone to environmentally induced fertility restoration and must be carefully monitored in the field. Environmentally induced, in contrast to genetic, restoration occurs when certain environmental stimuli signal the plant to bypass sterility restrictions and produce pollen anyway. Genome sequencing of mitochondrial genomes of crop plants has facilitated the identification of promising candidates for CMS-related mitochondrial rearrangements. The systematic sequencing of new plant species in recent years has also uncovered the existence of several novel nuclear restoration of fertility (RF) genes and their encoded proteins. A unified nomenclature for the RF defines protein families across all plant species and facilitates comparative functional genomics. This nomenclature accommodates functional RF genes and pseudogenes, and offers the flexibility needed to incorporate additional RFs as they become available in future.