Grapevine is one of the most widely cultivated plants in the world and man has been growing it since the beginning of his recorded history. Despite this, haploid plants have never been observed in Vitis (Olmo, 1976), which would lead to the conclusion that haploidy, the ability to generate haploid (n) plants (sporophytes) rather than diploids (2n), is not a natural property of this genus. To understand the reasons for this inability, it is necessary first to analyse the general phenomena leading to haploidy and compare them with the genetic features of the genus Vitis.