This title is volume 83 of Memoirs of The New York Botanical Garden. The 26 papers comprising this volume were contributed by well–known palm researchers and reflect four themes: species and species concepts, species–level data, species–level case studies, and higher–level classification. Broad and narrow species concepts are provided and the usefulness of the different approaches discussed. Examples of species complexes illustrate the intractability of accounting for variation with conventional methods. The broad general differences in diversity between geographical areas are discussed, as are their possible causes.