© Humana Press, a part of Springer Science-Business Media, LLC 2009. All rights reserved. Population genetics is the study of evolutionary genetics at the population level focusing on the exchange of alleles and genes within and between populations as well as the forces that cause or maintain these exchanges. This exchange of genes and alleles causes changes in the specific allele and hence genotype frequencies within and between populations. Studying this evolution helps us to better understand how to use human populations as a data set to clarify genetic predisposition to disease. Even with all these discoveries in the field of population genetics and in the characteristics that cause population-based changes and their consequences (e.g., how genetics can affect human disease susceptibility), until recently, the advances in molecular biology and genetics had only enabled genotypes to be assessed one at a time by a technician in a laboratory. Now with the advent of the gene chips or microarrays, these methods can be automated and carried out at a much larger scale, i.e., 1 million genotypes per person on a single gene chip. The faster techniques will allow all genes to be tested for polymorphism within and between populations for many individuals in a population at a time and many populations at a time. The new technology will allow an even greater insight into the relationship between evolutionary forces and genetic changes in human populations.