Cyanobacteria are photosynthetic prokaryotes that have a variety of biological activities and can be used as dietary supplements. Because of its high nutritional, protein, and digestibility content, it is utilized as a meal supplement. Spirulina sp., Anabaena sp., Microcystis sp., Nostoc sp., Lyngbya sp., Oscillatoria sp., and other cyanobacteria create a wide range of secondary bioactive metabolites with diverse biological functions. Cyanobacteria produce various physiologically active and chemically diverse compounds such as saccharides, fatty acid amides, lipopeptides, cyclic and acyclic peptides, and alkaloids. More than half of marine cyanobacteria could be used to extract bioactive compounds that can destroy cancer cells by causing apoptosis. Their effectiveness as an antiviral, antitumor, antibacterial, anti-HIV, and dietary additive is extensively documented. However, such drugs are in various phases of clinical studies, and only a few have made it to the market. This chapter examines the bioactive chemicals in cyanobacteria with antiprotozoal, antibacterial, anti-inflammatory, anticancer, antioxidant, and antiviral properties. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023.