Genetic identity, or genetic relatedness, among relatives, is a key concept in kin recognition, which in turn is important in models for inclusive fitness and inbreeding avoidance. A mathematical definition is presented for the genetic identity based on the proportion of genome shared identical by descent by two relatives. The method of Guo [Am J Hum Genet 1995;56:1468-1476] is used to compute the variance of the genetic identity for various types of relationships. The method is versatile and can handle any kind of relationship. To illustrate the method, the standard errors of the genetic identity using published human genetic maps are computed.