1. Carbon (C): This is the backbone of all organic molecules. Carbon's ability to form four bonds with other atoms allows for the creation of long chains, rings, and complex structures.

2. Hydrogen (H): Hydrogen is frequently bonded to carbon, creating hydrocarbons. It also forms bonds with oxygen, nitrogen, and other elements in organic molecules.

3. Oxygen (O): Oxygen is found in many functional groups, such as alcohols, ketones, aldehydes, and carboxylic acids. It plays a vital role in biological processes like respiration and photosynthesis.

While these are the most common elements, others such as nitrogen (N), sulfur (S), phosphorus (P), and halogens can also be present in organic compounds.