2Graphene is a unique 2D nanostructured material with particles composed of few-nanometers thickness. Owing to its strength (130 GPa), Young’s modulus (1 TPa), enhanced thermal conductivity, and superior electronic properties, graphene acts as an outstanding reinforcing material today. Graphene is a multifunctional reinforcement that can improve the properties of polymers, even at extremely low loading. In addition, mechanical strength, a large surface area, easy functionalization, and other attractive physiochemical characteristics of graphene endorse its broad exploits in sensing/biosensing applications. A graphene-based polymer nanocomposite possesses exceptional properties such as mechanical, electrical, gas barrier, thermal, and flame-retardant properties than a neat polymer. Graphene-reinforced polymer composite–based biosensors have the advantage of higher sensitivity, with selectivity, fast response time, stability, and a low limit of detection (LOD). The exceptional properties of graphene-reinforced polymers can demonstrate superior performance in numerous applications such as electronic devices, memory devices, and semiconductive sheets in transistors, hydrogen storage, flexible packaging, and structural components for transportation or energy, aerospace, and printable electronics. This chapter highlights several graphene-based polymer nanocomposites for sensing applications, which include sensing of dopamine (DA), glucose, ammonia, hydrazine, nitric oxide, guanine, adenine, hemoglobin, methane, and formaldehyde gas.