Despite the importance of whiteflies as agricultural pests, few published studies have examined adult whitefly feeding behavior in the detail that can be obtained with electronic feeding monitor techniques. The objectives of this paper are to summarize what has been learned of whitefly feeding behavior from these studies, and to provide the biological meanings of the different electronic waveforms that feeding whiteflies produce, so that other researchers may be able to interpret the waveforms and use this powerful technique to answer critical questions regarding whitefly host selection and virus acquisition and inoculation. The studies summarized in this chapter used both DC and AC electronic recording techniques. Waveforms have been identified that correlate with the following processes: intercellular penetration of the stylets through plant tissue, puncture of stylets into cells, partial withdrawal and re-insertion of the stylets during a penetration, phloem ingestion, xylem ingestion, and oviposition.