Peanut is an allergenic legume that can cross-react with other plant-based foods, notably other legumes and tree nuts. Peanut-allergic individuals can be both cosensitized and coallergic to such items, requiring foresight when eliciting a clinical history of a reaction, in the diagnostic evaluation of such allergies, and in the counseling of patients as to food avoidances after a diagnosis is made. Legume allergens belong to the Fabaceae family and encompass the cupin, prolamin, PR-10, and lipid transfer protein families, which mediate cross-sensitization including that between peanut and tree nut. Among legumes, the most common patterns of clinical cross-reactivity are between peanut and lupine, peanut and soy, as well as chickpea and lentil, though this is highly dependent on geography and prevalence of these foods in the diet. Issues of cross-sensitization may exist between peanut and certain tree nuts, as well as among tree nuts though such patterns do not always result in clinically relevant allergy. Molecular diagnostic testing may be a future tool to help parse out the aforementioned patterns, but oral food challenges are still the gold standard for accurate diagnosis. Although potential desensitization treatments have emerged for peanut allergy, these have not been developed for other legumes and most tree nuts, and desensitization to peanut has not proven to have an effect on legume cross-sensitization.