Nitrosamines are compounds having the general structure R1N(-R2)-N=O. They are formed by oxidation of the amine (usually secondary or tertiary) with a nitrosating compound (nitrous anhydride) in a process called nitrosation. About 90% of them are carcinogenic to most experimental animals and they are reproductive toxicants. They are indirect carcinogens, which means they are activated by biotransformation in humans. The active forms of the compounds are different alkylating agents forming DNA adducts. They are particularly effective when they are absorbed over a long period in small doses. Nitrosamines are found in food, products made from malt, tobacco, rubber products, cosmetics, water, air, agricultural chemicals, and the work environment in engineering industry, in tanneries, in the rubber industry and in the production of rocket fuel. In addition, they may also be formed in humans in vivo. Humans are exposed to convincingly highest concentrations of nitrosamines through smoking and tobacco products, but most often through diet that includes cured meat, fried food, smoked canned food, food subjected to drying, cheese, fish products and beer. Processed meat is associated with colorectal cancer, however, consuming these foods in normal amounts will not have an adverse effect on health if principle of varied and moderate diet that includes e.g. fiber and antioxidants is applied. Nitrosamines in drinking water, air, cosmetics and rubber products are present in quite low concentrations, while in the workplace levels of exposure can be higher. Present amounts of nitrosamines are less alarming than they were in the past, but caution is still needed. Some of the named categories are now strictly controlled and do not pose a great danger while others expect a further control and setting up legislation so the situation can stay under control.