Recent advances in molecular genetics make the sequencing of genes a straightforward exercise. Comparisons of sequenced genes from different individuals of a species, or from different species, allow the construction of family trees or evolutionary trees which reveal genetic relationships. This volume shows for the first time how those trees, or phylogenies, can be used to answer questions about population dynamics, epidemiology, development, biodiversity, conservation, and the evolution of genetic systems. The techniques for deciding what these new trees can tell us come together in a unified framework so that a common set of methods can be applied, whatever area of biology interests the research worker.