Biological weapons are weapons that are living organisms. When used, it is a deliberate act to cause great harm and disease. Biological weapons tend to be concentrated. With this concentration, a small amount can cause extensive and widespread casualties. This chapter reviews the medical effects of biological weapons, emphasizing emergency care and management, recognition and identification of biological patients, and self-protection and decontamination when caring for a patient. Biological agents for warfare or terrorism are disease-causing organisms that are collected, processed, and delivered for maximum effect. Biological agents are divided into four groups: (1) pneumonia-like agents; (2) encephalitis-like agents; (3) biological toxins; and (4) other agents. Some specific agents profiled are pneumonia-like agents such as, Anthrax, plaque, Tularemia, and Q Fever; Encephalitis-like agents such as, Smallpox, Venezuelan Equine Encephalitis, Cholera, Brucellosis, and viral hemorrhagic fevers; biological toxins such as, Botulinum, Staphylococcal Enterotoxin B, Ricin, and Trichothecene Mycotoxins. When faced with a biological patient, several important emergency care principles are necessary and include, recognition and identification, isolation, supportive care, antibiotic and antitoxin therapy, and immunization and prophylaxis. Triage and decision making for biological patients are critical for the EMS provider facing mass casualties. Patients must be classified as minimal to moderate and severe. However, it is essential to reassess and re-triage patients continually as deemed necessary. Tables