The impact of sensors can be felt in every step of human life. Different kinds of sensors are being employed every day by academic researchers and industries for electrochemical and strain sensing applications. This chapter elucidates the significance of sensors and the type of sensors designed, developed and implemented to date. The categorization of sensors has been primarily done in two groups, including microelectrochemical-based silicon sensors and flexible sensors. The focus has been given towards flexible sensors, in which the raw materials and fabrication processes used to form the electrodes and substrates of the prototypes have been explained. Finally, some of the significant applications for flexible sensors have been shown in the chapter.