This chapter explains how to build a phylogeny for a certain set of species. A phylogenetic tree is a representation of species interrelatedness and conveys information about which taxa share recent common ancestors, which evolutionary groups (clades) species belong to, and the distances (time, genetic, or character differences) separating species. The chapter first considers two R packages called ape and picante for use in analysis of the R phylogenetic object (referred to as a phylo object type), along with a few other packages, before discussing the steps in reconstructing phylogenetic relationships. It also evaluates some tree-building approaches that are easily implemented in R, including distance-based methods and maximum likelihood methods. Finally, it describes ways of finding and adapting available phylogenetic trees, together with tree scaling and rate smoothing.