A biosensor is a self-reliant integrated device that is proficient in providing specific quantitative or semi-quantitative analytical information. It has been using a biological recognition component that is in direct spatial contact with a transduction component. It is an appliance that consists of two main parts: a bioreceptor and a transducer. Bioreceptor is a biological component that recognizes the objective of an analyte and a transducer. A physicochemical detector component has also been employed that converts the recognition incident into a measurable signal. All the biological materials including enzymes, antibodies, nucleic acids, hormones, receptors, organelles, or whole cells can be used as sensors or detectors in a device. Biosensors can provide low-priced and highly capable devices for being used in other day-to-day applications. It has multifarious potential applications of various types such as monitoring of treatment, disease progression, drug discovery, food control, and environmental monitoring as well as it continues to play a crucial role across numerous fields including biomedical diagnosis. In this review, we give a general introduction to biosensors and their applications, including a brief historical overview. Keywords: Biosensor, Bio-receptor, Transducer, Analyte, Detector.