This chapter is an extensive overview of microorganisms as innovative biosensing tools for monitoringMonitoring environmentalEnvironmental pollutantsPollutants, stressing their mechanisms, applications, and imminent prospects. It explores how genetically modified microbial cells and whole cells detect a varied range of environmentalEnvironmental pollutantsPollutants, including heavy metalsHeavy metals, hydrocarbons, pesticides, and volatile organic compounds, in waterWater, soilSoil, and air with great sensitivity and specificitySpecificity. Major case studies that demonstrate the roles of microbial biosensorsBiosensor in tracking biogeochemical cycling and measuring the bioavailability of pollutantsPollutants are also presented in this chapter, with emphasis on advantages such as rapidity, cost-efficiency, and in situ real-time analysis. The chapter further addresses critical encounters that include the stability of microorganisms, biosafety regulatory issues, and complex environmentalEnvironmental matrix interferences. Going forward, the chapter presents emergent tactics for improving the robustness of the microbial biosensorsBiosensor, expanding their use to extreme environments, and integrating them into citizen science and community-based environmentalEnvironmental assessment and monitoring frameworks. Ultimately, this chapter emphasizes the transformative prospects and potentials of microbial sensors for the advancement of environmentalEnvironmental sustainability via real-time, biologically relevant monitoringMonitoring and democratization of data.