This chapter reviews the basic measures of intraspecific population subdivision, without assuming any particular spatial model. The structure of the chapter follows from the historical development of the field, starting with the presentation of Wright's fixation indexes as correlations of gene frequencies, then Nei's extension of F-statistics to multiple alleles as function of heterozygosities and his introduction of G-statistics as function of gene diversities, and ending with Cockerham's intraclass correlations obtained under an analysis of variance framework. We also present an extension of the analysis of variance approach to handle molecular data (DNA sequences, microsatellites) as well as dominant data. The relationships between different estimators, different approaches and their potential limitations are discussed.