Different hypotheses have been formulated on the history and geographical origin of citrus. It would appear that all the species belonging to Citrus and its related genera originated in the tropical and subtropical regions of South-east Asia, north-eastern India, southern China, the Indo-Chinese peninsula and the Malay Archipelago, and then spread to other continents. Several authors consider that the primordial genetic nucleus of citrus originated in China and the citrus slowly passed from its original location to other oriental regions and from there followed the paths of civilization.The majority of taxonomists consider that citrus species belong to the Geraniales order, the Rutaceae family and the Aurantioideae subfamily. The taxonomic situation of tribes, subtribes, genera and species within the Aurantioideae is controversial, complex and sometimes confusing. The first descriptions and classifications of citrus species and varieties date back to the seventeenth century, while the morphological description of the trees, the floral morphology and biology or the different use of the fruit date back to ancient times (Teophrastus 310 BC, Virgil 70-19 BC, Pliny 27-79 AD etc.). John Baptista Ferrarius in 1646 made the first organic contribution to citrus studies followed by Volkamer (1708), Linneus (1767), Burmann (1768), De Loureiro (1790), Gallesio (1811), Risso (1813), and many others. Today two different classification systems are commonly accepted for the citrus taxonomy: the system of Swingle (1943, 1967) and that of Tanaka (1954, 1961). Taxonomic studies received a boost from the work of Barrett and Rhodes in 1976. Their study suggested that only three citrus types, namely the citron, Citrus medica, the mandarin, Citrus reticulata and the pummelo, Citrus grandis, constituted true or valid species. The concept of the true valid species and the other genotypes derived from hybridization between them, has gained further support from various studies using biochemical and molecular markers. Several authors in the recent years have studied the phylogenetic relationships in Citrus, analyzing the relationships among hundreds of accessions of Citrus and related genera. Moreover a lot of hypotheses have been formulated on the genetic origin of the main citrus species. The present study examines the results achieved by now.