**Abstract**

Paradoxically, continuous vegetative multiplication of traditional grapevine cultivars aimed to maintain cultivar attributes in this highly heterozygous species ends in the accumulation of considerable somatic variation. This variation has long contributed to cultivar adaptation and evolution under changing environmental and cultivation conditions and has also been a source of novel traits. Understanding how this somatic variation originates provides tools for genetics-assisted tracking of selected variants and breeding. Potentially, the identification of the mutations causing the observed phenotypic variation can now help to direct genome editing approaches to improve the genotype of elite traditional cultivars. Molecular characterization of somatic variants can also generate basic information helping to understand gene biological function. In this chapter, we review the state of the art on somatic variation in grapevine at phenotypic and genome sequence levels, present possible strategies for the study of this variation, and describe a few examples in which the genetic and molecular basis or very relevant grapevine traits were successfully identified.

**Keywords:** somatic variation, genome sequence variation, somatic mutations, chimerism, Meunier phenotype, fruit color variation, seedlessness, Muscat aroma, forward genomics
