Forkhead box (Fox) proteins are transcriptional factors, designated as the unified symbol for all chordate winged helix/forkhead transcription factors by Forkhea/Winged Helix nomenclature committee, and issued in the year of 2000. To date, over 100 forkhead genes have been identified in organisms ranging from yeast to humans. The importance of FOXO subfamily of Fox proteins in the fields of animal lifespan, reproduction, metabolism, oncogenesis and immunity, the nomenclature and taxonomy of Fox proteins are reviewed. In addition, the molecular structure of Fox proteins and chemical modification and regulation of FOXO subfamily is summarized. Furthermore, the functions of FOXO proteins in apoptosis and oncogenesis are discussed.