 Metal organic frameworks, MOFs, are a type of crystalline coordination polymer composed of metal ions or clusters and organic ligands. These materials have been used to develop sensors for detecting environmental contaminants such as anions, heavy metals, organics, and gases. Recent advances in MOF-based sensors include optical, electrochemical, and field effect transistors. These sensors have demonstrated unique and promising performance in water and gas contaminant sensing. Additionally, MOF-based composites can be used to further enhance the sensor performance. Finally, the current limitations and future directions of MOF-based sensors are discussed. This article was authored by Xian Fang, Boyang Zong, and Shen Mao.