The molecules which are produced by living animals are known as biomolecules. It includes large Macromolecules like protein, enzymes, vitamins, carbohydrates, lipids, polysaccharides, nucleic acids, small molecules like metabolites, and natural products. These molecules are also known as biogenic substances. Biomolecules are the organic compounds present as essential constituents of the living organism in different cells. These biomolecules interact with each other and constitute the molecular logic of life processes. Also, some simple molecules like vitamins and mineral salts play an essential role in the functions of organisms. After studying this chapter, students will be able to explain the characteristics of biomolecules like carbohydrates, proteins and nucleic acids and hormones. Classify carbohydrates, proteins, nucleic acids and vitamins based on their structures; explain the difference between DNA and RNA and describe the role of biomolecules in bio-system.