Citrus Taxonomy. Challenges to the Citrus Industry. Part I: Genetic Diversity in Citrus. Challenges and Advances in Citrus Breeding. Genetic Improvement in Citrus. Part II: Abiotic Stresses and Citrus: Physiology, Metabolic and Molecular Responses. Citrus Response and Tolerance against Salinity. Drought. Water Logging. Temperature Stress. Light Stress. Heavy Metals. Nutritional Imbalance. Part IV: Recent Biotic Stresses Faced by Citrus Production. Citrus Greening. Citrus Response to Diseases. Insects that Threaten Citrus Production. Part V: Harvest and Postharvest Challenges. Harvesting Factors that Influence Citrus Production. Preharvest Conditions that Influence Postharvest Losses. Post-harvest Physiology and Quality Maintenance of Citrus Fruit. The Supply Value Chain of Fresh Citrus Fruit. Citrus Nutritional Value and Human Health.