A bioreactor is a vessel or container used to grow and cultivate living cells or microorganisms under controlled conditions. These systems are essential in various fields, including biotechnology, pharmaceuticals, and environmental engineering, as they facilitate the production of products like vaccines, enzymes, and biofuels. Bioreactors can vary in size and design, ranging from small laboratory setups to large industrial units. They maintain optimal conditions such as temperature, pH, and oxygen levels to maximize cell growth and productivity. Common types include stirred-tank bioreactors and fixed-bed bioreactors, each suited for specific applications.