Reconciling the genetic, linguistic and archaeological histories of humans will require linguists and geneticists to interact in the design and implementation of future research strategies. This paper discusses the issues involved in correlating these disciplines and highlights some of the problems involved. It is argued that correlation cannot be an a priori assumption, but must be proved prior to or as part of each investigation. An urgent need for hierarchical linguistic classifications is established and several possible methods are identified. Case studies include the Indo-European language family and Eurasian populations; the Nostratic hypothesis; and the history of Austronesia. General and specific factors responsible for correlations, or their absence, are considered in relation to autosomal, mitochondrial and Y-chromosome-specific data and human demography.