Introduction to Cladistics: Cladistics is a particular method of hypothesizing relationships among organisms based on the idea that members of a group share a common evolutionary history.
Phylogenetics Methodology: Introduction to various phylogenetic statistical methodologies.
Understanding Cladistics: Short introduction from the American Museum of Natural History.
What is Cladistics?: The methods and terminology of phylogenetic systematics explained by the magazine Fossil News.
Willi Hennig Society: Society of scientists studying cladistics.