A discussion of biohazards was presented in this chapter. Infectious biohazards were classified as agents of human origin, animal origin, or other. Human biohazards included the hepatitis-B virus, rubella virus, respiratory syncytial virus, herpes simplex virus, influenza viruses, Mycobacterium-tuberculosis, Salmonella, and Staphylococcus-aureus. Animal biohazards included the Orf virus, foot and mouth virus, Coxiella-burnetii, Chlamydia-psittaci, Trichophyton-verrucosum, brucellosis, and Schistosoma, among many others. The group of other infectious agents included viruses, bacteria, and protozoa that are found in sewage, water and geophilic fungi. Noninfectious biohazards included substances that result in allergic reactions after exposure. These allergenic biohazards may be derived from microbes, plants, or animals. A list of occupational groups at risk for exposure to such allergenic biohazards was presented, and the effects of such biohazards on humans were discussed.