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 (saltpeter) and ammonium nitrate are an important source of nitrogen in fertilizers. These nitrates must be used quickly by plants because they are easily lost through leaching or denitrification by bacteria. Nitrate pollution has become an environmental issue in rivers and oceans. According to the Black Hawk County Green Party, the Cedar River (Iowa) has the highest nitrate levels of any river in the world.

Nitrates are also oxidizing agents. 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, isosorbide mononitrate (ISMN) and isosorbide dinitrate (ISDN) are particularly useful for prevention and treatment of angina pectoris. However they can cause a dangerous reaction if taken within 24 hours of taking sildenafil citrate (Viagra®) or similar drugs.

Nitrates covered in Wikipedia include:

• ammonium nitrate
• calcium nitrate
• lead(II) nitrate
• lithium nitrate
• magnesium nitrate
• potassium nitrate
• silver nitrate
• sodium nitrate
• isosorbide mononitrate
• isosorbide dinitrate

Nitrates should not be confused with nitrites, the salts of nitrous acid. Organic compounds containing the nitro functional group (which has the same formula and structure as the nitrate ion) are known as nitro compounds.