Food allergy remains a major problem affecting consumers. Together with peanut, tree nuts belong to a small group of allergens responsible for the great majority of food allergies. This chapter begins by providing an overview of tree nut allergies and their prevalence. It then discusses allergenic proteins and thresholds, as well as the required sensitivity of detection methods. Finally, the chapter reviews both general issues in developing effective detection methods as well as the range of techniques available for particular tree nuts, and looks ahead to future research trends in this area.