Hazardous material classifications are consistent across all agencies who regulate commercial shipping and are based on criteria developed by the United Nations (UN) Committee of Experts working with the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC), medical professionals, microbiologists, transportation professionals, and packaging technical experts. These requirements can be found in the 13^th and 14^th editions of the United Nations Recommendations for the Transport of Dangerous Goods, the 2005 - 2006 edition of the International Civil Aviation Organization Technical Instructions for the Safe Transport of Dangerous Goods by Air (ICAO Technical Instructions), and the International Maritime Organization (IMO) Dangerous Goods Code.

The classification system for Division 6.2 Infectious Substances includes two catergories, known simply as Category A and Category B.