The expansion of cities and industrialization are the major reasons for environmental pollution, due to the harmful chemicals emitted by industries and urban cities into the atmosphere. Air, water, soil, and other forms of pollution have increased as a result of the expanding urbanization and industrialization tendencies. Pesticides, fertilizers, and pharmaceuticals released by mining and metallurgy, textile and dyeing, pulp and paper, waste management and landfills, and electrical device manufacturers are the main sources of industrial pollutants that pollute the environment. These businesses damage the ecosystem and cause serious health problems for people by releasing hazardous chemicals, waste products, and heavy metals into the air, water, and land. The health issues increase due to bad air quality, spoiled drinking water, and soil pollution. A preventive method to overcome this environmental pollution, a biological technique known as “bioremediation,” has come into existence. The technique involves microorganisms that perform degradation and transformation, detoxification, and immobilization of pollutants in soil, water, and other growth media. Microorganisms are the primary and significant agents in the process of bioremediation due to their adapting ability under any environmental circumstances and various metabolic capabilities that degrade different pollutants. Bioremediation involves the most relevant technique known as degradation. Different microbes develop different mechanisms for degradation through biosorption, biotransformation, and bioaccumulation, for bioremediation based on the particular pollutant degradation. The success rate of bioremediation is based on the type of microorganisms employed in the degradation process, the nature of the contaminant and its concentration, and the prevalent environmental circumstances. This chapter gives a definite explanation of the function of microorganisms in bioremediation, assessing their significance in various types of pollutant degradation and transformation processes—inorganic or organic—which occur when heavy metals are present.