The immune response against helminths and allergens is generally characterized by high levels of IgE and increased numbers of Th2 cells, eosinophils, and mast cells, yet the clinical outcome with respect to immediate hypersensitivity and inflammation is clearly not the same. High levels of IgE are seen to allergens during helminth infections; however, these IgE responses do not translate into allergy symptoms. This chapter summarizes the evidence of the association between helminth infections and allergic disorders. It discusses how helminth infection can lead to IgE cross-reactivity with allergens and how this IgE has poor biological activity. This information is important for developing new diagnostic methods and treatments for allergic disorders in low-to-middle-income countries.