This chapter surveys the wide-ranging applications of phylogenetics. It demonstrates how trees aid in taxonomy, systematics, conservation biology, historical biogeography, phylogeography, epidemiology and the study of character evolution. Examples include detecting cryptic species, tracing dispersal routes, resolving speciation modes and reconstructing the evolution of genes, traits and behaviours. The chapter shows how phylogenies inform conservation priorities by revealing evolutionary distinctiveness and uncovering hidden diversity. The chapter ends with a brief explanation on phylogenetically independent comparison and phylogenetic comparative methods and their applications.