The United States spends billions of dollars annually in education, research, containment, and eradication programs for introduced insect and plant pathogen pests. Recent insect introductions include the emerald ash borer, Sirex woodwasp, Asian longhorned beetle, several exotic bark and ambrosia beetles, pink hibiscus mealybug, glassy-winged sharpshooter, and soybean aphid. These insects cause direct damage to their plant hosts, however the latter two insects also serve as vectors of important plant pathogens. The glassy-winged sharpshooter, native to the southeastern U.S. and only introduced to California within the last 10-15 years, vectors the Xylella bacterium that causes Pierce's disease in grapes. The soybean aphid vectors certain viruses including soybean mosaic virus. Due to large host ranges, some of the hardwood pest introductions may cause more long term damage to our forest and urban landscapes than either Dutch elm disease or chestnut blight if left unchecked. Threats to plant based systems in the United States will be discussed with an emphasis on diagnosis.