Release of toxic chemicals or pollutants like heavy metals, pesticides, aromatic hydrocarbons, and pharmaceutical products contributes heavily to environmental pollution. Hence, the rapid detection of these pollutants is necessary to reduce possible environmental pollution. Biosensors can be excellent and highly specific tools for detecting pollutants in the environment, which possess significant impacts on ecosystems, human health, and development. Different types of biosensors have been developed for the purposes of pollutant monitoring. This chapter focuses primarily on whole-cell-based biosensors for detecting environmental pollutants. Cell-based biosensors are developed by fusing reporter genes such as lacZ, lux, and gfp, with inducible regulatory genes that react to specific environmental pollutants, like heavy metals and aromatic hydrocarbons. A broad range of microbial biosensors has been developed by using novel recombinant DNA technology.