Bioremediation is an ecologically sound and state-of-the-art technique that employs natural biological processes to completely eliminate toxic contaminants. Any process that uses microorganisms, fungi, green plants or their enzymes to return the natural environment altered by contaminants to its original condition. Bioremediation technologies can be generally classified as in situ or ex situ. In situ bioremediation involves treating the contaminated material at the site while ex situ involves the removal of the contaminated material to be treated elsewhere. Some examples of bioremediation technologies are bioventing, land farming, bioreactor, compositing, bioaugmentation, rhizofiltration, and bio-stimulation. Microorganisms which perform the function of bioremediation is known as bioremediators. Not all contaminants, however, are easily treated by bioremediation using microorganisms. For example, heavy metals such as cadmium (Cd) and lead (Pb) are not easily absorbed or captured by organisms. The assimilation of metals such as mercury into the food chain may worsen matters. This manuscript gives an idea of what is bioremediation, principles of bioremediation, factors of bioremediation strategies, types, genetic engineering approaches, monitoring bioremediation and advantages or disadvantages of bioremediation.