The i PhyClassifier is an internet-based research tool for quick identification and classification of diverse phytoplasmas. The i PhyClassifier simulates laboratory restriction enzyme digestions and subsequent gel electrophoresis and generates virtual restriction fragment length polymorphism (RFLP) patterns. Based on RFLP pattern similarity coefficient scores, the i PhyClassifier gives instant suggestions on group and subgroup classification status of the phytoplasma strains under study. The i PhyClassifier also aligns the query sequences with that of reference strains of all previously described ‘Candidatus Phytoplasma’ species, ?calculates sequence similarity scores, and assigns the phytoplasmas under study into respective ‘Ca . Phytoplasma’ species as related strains according to the guidelines set forth by the Phytoplasma Taxonomy Group of the International Research Program on Comparative Mycoplasmology. Additional functions of the i PhyClassifier include delineation of potentially new phytoplasma groups and subgroups as well as new ‘Ca . Phytoplasma’ species. This chapter describes the program components, the operational procedure, and the underlying principles of the i PhyClassifier operation. The chapter also provides hints on how to interpret the results.