A Haz Mat (hazardous material) is any solid, liquid, or gas that can harm people, other living organisms, or the environment. The term hazardous material is used in this context almost exclusively in the United States. The equivalent term in the rest of the English-speaking world is Dangerous Goods. A hazardous material may be radioactive, flammable, explosive, toxic, corrosive, biohazardous, an oxidizer, an asphyxiant, an allergen, or may have other characteristics that make it hazardous in specific circumstances.

Laws and regulations on the use and handling of hazardous materials may differ depending on the activity and status of the material. For example one set of requirements may apply to their use in the workplace while a different requirements may apply to spill response, sale for consumer use, or transportation. Most countries regulate some aspect of hazardous materials.