This book provides a comprehensive and in-depth examination of citrus flavonoids, detailing their classification, optimized methods for identification and extraction, biological activities, and the key biosynthetic genes and metabolic pathways involved in citrus. As the world’s most widely produced fruit, citrus attracts broad scientific interest due to its nutritional value, with flavonoids serving as its representative bioactive components. This book establishes a solid framework for understanding citrus flavonoids by emphasizing research methodologies, evaluation strategies, and the intrinsic connections between phenotype and mechanism in both biological activity and biosynthesis. This book serves as a valuable resource for undergraduate and graduate students interested in citrus and natural products, as well as for researchers and professionals working in agriculture, botany, horticulture, food science, pharmacy, medicine, and secondary metabolite biosynthesis.