Cast differentiation allows individuals with the same genome to develop different morphology and behavioral characteristics. Honeybee queens and workers have essentially the same genome, but develop distinctly different morphology, physiology, roles within the colony and life span, due to differences in nutrition and brood cell size during larval development. The major factors underlying cast differentiation remain unclear. This article reviews progress in research on the main factors affecting caste differentiation in honey bees, including nutrition, developmental space, protein expression, gene expression, methylation, and hormone regulation, and suggests directions for future research.