Every organic molecule contains carbon. The different classifications of organic compounds are determined by the number of carbon atoms within the compound, the type of bonds they form with one another, and the type of bonds they form with other elements.
Organic molecules commonly contain one or more carbon-hydrogen bonds, making hydrogen the second most common element in an organic compound.
Many biological molecules associated with life processes are organic, including DNA, fats, sugars and proteins. Fuel sources such as methane and alcohols are also organic compounds. The opposite of organic molecules are inorganic molecules, which do not usually contain carbon.