Biological weapons are weapons of mass destruction based on bacteria, viruses, rickettsiae, fungi, or toxins produced by living organisms. Biological weapons can be deployed in three ways: (1) contaminating food or water supplies; (2) the releasing of infected vectors; or (3) by creating an aerosol cloud to be inhaled by victims. The most effective mode of application of biological weapons is an aerosol cloud. Several countries have produced biological weapons for military use, such as the United States and the former Soviet Union. The Soviet Union's biological weapons program began in the late 1920's and the United States had a biological weapons program until 1969. The Soviet's viewed the best biological agents as those where there were no prevention or cure. With the collapse of the Soviet Union in 1992, a decree was signed banning all biological weapons-related activity. However, there were reasons for concern that the biological weapons program continued in Russia. The interest in biological weapons by terrorist groups has been of no surprise among the world leaders. Their interest has been on the level of state-sponsored terrorist organizations. Due to the former Soviet Union and Russia's powerful biological weapons programs, former Soviet scientists have become very useful to military and terrorist organizations. In addition, a potent mix for future biological weapons development is biotechnology and information technologies. So, concentration should be on developing appropriate medical defenses, such as pretreatment, prophylaxis, and chemotherapy. The United States must increase efforts to develop new treatments and prophylaxis techniques, as well as new approaches in protecting against and treating a variety of pathogens.