Allergy to arthropods is a major social, economic, and medical problem. These animals are sources of allergens that sensitize and induce IgE-mediated allergic reactions. Important allergen sources from arthropods include Hymenoptera venoms, edible crustaceans, and body secretions, saliva, excreta, exoskeletons, and body parts of insects and mites. The preparation of arthropod allergen extracts, such as cockroaches, ticks, storage mites, spiders, mosquitos, red chironomid larvae, silverfish, and ladybugs as well as a variety of storage pests, is described in this chapter. The inhalation of skin-derived mammalian allergens is a common cause of allergic sensitization and allergic respiratory symptoms worldwide. Their sensitization may occur at home from allergens derived from cats, dogs, horses, cows, and rodents, and in research laboratories. Approximately 5450 species of mammals have been described. An important issue to consider when preparing allergen extracts of mammalian origin is that mammalian allergens can be present in different parts of the animals, including the hair, skin scrapes, dander, body secretions, saliva, the meat, feces, milk, and milk derivatives. Various methods of manufacturing allergen extracts and their clinical application for the diagnoses of sensitivities to mammalian- and arthropod-derived allergens are discussed in this chapter. Allergen extracts are usually prepared by aqueous extraction of allergenic source material.