The potato leafhopper, Empoasca fabae (Harris), has developed from a little-known pest of alfalfa at the turn of the century to one of the most severe pests attacking the alfalfa crop today across most of the northcentral and northeastern United States. Various researchers soon identified alfalfa yellowing or “hopperburn” as the single most apparent indicator of potato leafhopper stress on alfalfa. Reduced number of stems, delayed maturity, reduced leaf size, leaf drop, and leaf death are other growth characteristics that have been attributed to the potato leafhopper feeding on alfalfa. Losses in protein, crude fiber, digestible dry matter, and other chemical changes have been attributed to this pest. Although many of the early researchers reported its effect on yield of the currently infested crop, only a few suggested more severe or long-term detriment caused by this insect’s feeding. Previously infested plants exhibited significantly less growth the following spring. Likewise, it had been reported that seedling damage by this pest reduced yield the subsequent year and certain varieties of alfalfa lost their winter hardiness following potato leafhopper attack. In addition, plants stressed by the potato leafhopper have reportedly developed more root rot. The degree of damage caused by the potato leafhopper is influenced by insect and crop parameters. Insect numbers, age, and sex, as well as crop age at the time of infestation, influence the effect of this insect on alfalfa. Furthermore, field conditions such as low soil fertility and inadequate soil moisture compound the effect of the potato leafhopper on alfalfa growth. Although it has been documented that the potato leafhopper causes loss in alfalfa biomass and affects certain alfalfa quality parameters, little information exists on how the potato leafhopper more specifically influences the alfalfa growth processes. Reduced photosynthesis and respiration in the potato plant and alfalfa as a result of potato leafhopper feeding have been reported. Blockage of the transport vessels as described for potato leafhopper feeding could influence the accumulation of leaf carbohydrates in alfalfa infested with potato leafhopper. A better understanding of this insect as a stress on alfalfa photosynthesis, transpiration, and assimilate partitioning will improve our understanding of the pathways by which this insect’s feeding influences alfalfa growth. Improvement of our understanding of the potato leafhopper-alfalfa interaction will serve to develop more meaningful management programs for this important pest.