A bioreactor is the unit of biological process which holds biologically active environment. It is a vessel which contains biological materials used for growing organisms (yeast, bacteria or animal cells) under controlled conditions ensuring the same temperature, pH and O levels. Their sizes differ from few mm3 to 500 m3. The various kinds of bioreactors which have different industrial applications. This review extensively focuses on the different types of bioreactors and their applications in the bio-transformation of the enzymes (amylase, lipase, cellulose etc.), medicines and recombinant proteins.