Organophosphorus compounds belong to an important class of pesticides and have widely been used in different areas such as agriculture, medicine, industry, and chemical warfare. Commonly used organophosphorus compounds include malathion, diazinon, parathion, methyl parathion, chlorpyrifos, and dichlorvos. Some of the organophosphorus compounds do not decompose easily and thus migrate from soil to water sources. Due to their high toxicity, persistence, and accumulation in the food chain, the excessive use of these organophosphorus pesticides could result in environmental pollution and other ecological problems. Also, their presence in water and food could lead to increased hazards to human health. Analytical techniques, such as high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS), employed for the detection of organophosphorus pesticides are very sensitive and reliable, but they require high-end large-scale instruments and equipment and are also very time-consuming. Therefore, to overcome these problems, nanotechnology has emerged as a powerful tool for detection of organophosphorus pesticides. Polyaniline nanowires network, an acetylcholinesterase biosensor based on conducting polymer using multiwalled carbon nanotubes (MWCNTs) and graphene-polyvinyl alcohol nanocomposite, Au-ZrO2-SiO2 nanocomposite spheres, and nanostructured photoelectrochemical biosensors have been extensively used for the detection of organophosphorus pesticides. This chapter mainly focuses on structures and activities of organophosphorus compounds used as pesticides and their different detection methods employing nanomaterials.