Phylogenetic trees, which are depictions of the inferred evolutionary relationships among a set of species, now permeate almost all branches of biology and are appearing in increasing numbers in biology textbooks. While few state standards explicitly require knowledge of phylogenetics, most require some knowledge of evolutionary biology, and many scientists and educators would hold that it is impossible to really understand evolution without an ability to accurately interpret phylogenetic trees. Research suggests that students hold significant misconceptions about trees and that these views may be deeply held and persistent. Therefore, the challenge faced by teachers, most of whom have had little exposure to phylogenetics, is significant. In this article, the authors provide a brief overview of some important principles of tree-thinking and a list of specific skills in which high school and college students should become proficient. They also discuss strategies for bringing trees into the broader biology curriculum. (Contains 1 table and 10 figures.)