Algae are referred to a diverse class of eukaryotic being with a load source of different bioactive compounds. Thus, primary metabolites are indispensable component of algal cells, with critical roles including evolution, growth, and survival. This chapter discusses the primary metabolites found in algae, especially carbohydrates, lipids, nucleic acids, and proteins. The biogenesis and usefulness of these metabolites with highlights of their importance in algal physiology and ecology are exploited. The potential applications and innovations of algal primary metabolites in different economic purposes, such as biofuels, food, and pharmaceuticals, are explored. Conclusively, comprehensive understanding of the primary metabolites of algae with emphasis on their significance in both basic and applied research are reviewed.