Molecularly imprinted polymers are now well known as synthetic polymeric receptors or robust artificial antibodies (“plastibodies”) and have attracted considerable attention from the scientific and industrial community due to their inherent simplicity, reusability, robust polymer network, and cost-effectiveness. In this chapter, the concept and principles of molecularly imprinted polymers are introduced and illustrated. Their fascinating properties are further described and summarized with a focus on the medical/biological aspects followed by a comprehensive review of published research results on the sensor applications of molecularly imprinted polymers as biomaterials and/or biocompatible materials. In addition, a future outlook is presented demonstrating the great potentials of molecularly imprinted polymers for in vivo sensing.