This book gathers the information about the molecular phylogeny, antioxidant compounds and health benefits of citrus. It covers the biological aspects of citrus production and its ecological journey emphasizing on functional traits related to its nutritional and photosynthetic apparatus. The already published data has been reviewed and re-interpreted with an added ecological point of view that, perhaps, is not discussed by most of the textbooks or journals. The enzymes involved in the biosynthetic pathways of citrus bioactive compounds to modulate a variety of plant characteristics are debated. The information about the genetic architecture of citrus genome and the genes specifically involved in fruit development, in particular, related to antioxidant accumulation, are extensively discussed, which would help the citrus breeders to know precise information on the most important genes useful to develop improved cultivars.