1. Carbon (C): Carbon is the backbone of all organic molecules. Its ability to form four bonds with other atoms allows it to create long chains, branched structures, and rings, forming the diverse structures of organic compounds.

2. Hydrogen (H): Hydrogen is the most abundant element in organic molecules. It frequently forms single bonds with carbon, and is also found in various functional groups.

3. Oxygen (O): Oxygen is a common element in organic molecules, often found in functional groups like hydroxyl (-OH), carbonyl (C=O), and carboxyl (-COOH). It plays a crucial role in many biological processes, including respiration and photosynthesis.