1. Carbon (C): The backbone of all organic molecules. It has the ability to form four bonds, allowing for complex structures.

2. Hydrogen (H): The most common element found in organic compounds. It forms single bonds with carbon and other elements.

3. Oxygen (O): Often found in functional groups, oxygen plays a crucial role in many biological processes like respiration.

4. Nitrogen (N): Found in amino acids, proteins, and nucleic acids, nitrogen contributes to the complexity and diversity of organic molecules.