Nowadays, nanomaterials are considered a magic tool in many industrial applications. They offer smart solutions for problems related to health, the environment, and energy. Because of their tiny size and precise characters, nanomaterials represent a unique and vital component in microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS)-based technologies. One of the most important applications of these technologies is sensors. Sensors are divided into two main constituents, the first is the device and the second is the sensing materials. This chapter explains the main sensor components. It highlights the different classes of sensing materials. The main categories of sensing techniques are summarized. It also explains the relation between sensing materials and proposed sensing techniques, with a focus on materials properties at the nanoscale and their selective response to certain stimuli. Finally, it concludes with the challenges and prospective of the sensor industry and market.