Although both leafhoppers and spittlebugs have piercing sucking mouthparts, they feed on different parts of the plants. Leafhoppers feed on plant sap from xylem, or phloem, or mesophyll; but spittlebugs feed on plant sap only from xylem. Most leafhoppers and a few spittlebugs are agricultural pests due to they can transmit plant-infecting bacteria, especially the leafhoppers also can transmit plant infecting phytoplasma or virus. Thus, the taxonomy on the two families is extremely important. The total numbers of species for the families Cicadellidae (so called leafhoppers) and Aphrophoridae (one kind of spittlebugs) are 25000 and 900 species respectivelyin the world, of which 374 cicadellid and 73 aphrophorid species are recorded from Taiwan. Before 1940, Shonen Matsumura did most of the taxonomic studies on the Taiwanese leafhoppers and spittlebugs. The rest works were mainly done by Masayo Kato and F. Schumacher. At that time, taxonomists established new taxa usually based on a few morphological characters and coloration patterns, and described unclear species delimitations by no comparisons with allied species. Furthermore, the information on the type deposition of Kato’s type specimens is still unknown. Most of taxonomic problems above have a great effect upon the subsequent taxonomy on leafhoppers and spittlebugs of Taiwan and eastern Asia. After 1941, the taxonomy of Cicadellidae and Aphrophoridae of Taiwan had not been studied about 30 and 50 years respectively. Then, taxonomies of Cicadellidae and Aphrophoridae are studied again by some taxonomists from 1970, e.g. C. C. Chiang, K.W. Huang, H. T. Shih, and a few foreign taxonomists. At present time, Cicadellidae and Aphrophoridae of Taiwan are revised taxonomically based on the male genitalia;in addition, the diagnostic characters on subfamilial or generic category and identifications of agriculturally economic species will also be done in near future.