Citrus is the most important fruit tree crop in the world, with a production of more than 100 million tons annually. The area of origin of Citrus is believed to be southeastern Asia, where its domestication started. It has become clear that only citron, mandarin, and pummelo are true species within genus Citrus, being other important Citrus types, as sweet orange, sour orange, lemon, lime, grapefruit and other mandarins originated from hybridization between these ancestral species. In spite of the many efforts put in classical breeding programs in the last 100 years, current citrus industry relies on various groups of varieties that are grafted onto rootstocks adapted to different abiotic and biotic stresses. Most of these genotypes have been generated by chance, mostly as budsports but also as natural hybrids or seedlings selected by men in the wild or in orchards. Citrus breeding is complicated due to its complex reproductive biology. In this context, genetic transformation offers an important alternative for the genetic improvement of citrus. Moreover, it is probably the most efficient approach to make reverse genetics in citrus to investigate gene function and thus to gain better understanding in metabolic processes and plant‐pathogen‐environment interactions.