Nitrates are the salts of nitric acid. The nitrate ion is the polyatomic ion with chemical formula NO3; it is the conjugate base of nitric acid. The nitrate ion is planar and has the following structure:

     O     O
      \\\\  /
        N+
        |
        O

A nitrate salt forms if a positively charged ion attaches to one of the negatively charged oxygen atoms of the nitrate ion.

Nitrates such as potassium nitrate (saltpetre) and ammonium nitrate are an important source of nitrogen in fertilizers.

Nitrates are also oxidizing agentss. When mixed with hydrocarbons or carbohydrates, nitrates can form a flammable or even explosive mixture. For example, potassium nitrate is the oxidizing ingredient in black gunpowder.

In Medicine, Nitrates such as nitroglycerin and isosorbide mono- and di- nitrates are particularly useful for prevention and treatment of angina pectoris. However they can cause a dangerous reaction if taken within 24 hrs of taking Viagra or sildenafil citrate.

Nitrates covered in Wikipedia include:

Nitrates should not be confused with nitrites, the salts of nitrous acid.