Chemical sensors, or chemosensors, for detecting both negatively charged particles (anions) and positively charged particles (cations) have become indispensable across numerous fields, including pharmacology, environmental monitoring, biology, and chemistry. It focuses specifically on the design of systems that can identify and quantify these charged species by producing measurable signals, typically via optical (absorption or fluorescence properties) or electrochemical changes. The development of chemosensors remains an active and attractive area of research within supramolecular chemistry. This chapter specifically discuss the operational principles of chemosensor, the challenges inherent in their design and different mechanism by which chemosensor interact with the target analyte.