A piezoelectric medium provides an attractive technology for realizing a variety of sensors that exhibit high sensitivity, small size and portability, fast responses, ruggedness and robustness, excellent aging characteristics, high accuracy, and the capability to measure multiple quantities in a single sensor package. Sensors based on this technology can be produced using standard photolithography and, hence, are inexpensive. Piezoelectric sensors are fabricated from materials in which the electromechanical transduction takes place within the material. This material-based transduction process very positively influences the performance of acoustic sensors in terms of their reliability, size, and cost. Piezoelectric sensors are versatile and can measure, in principle, any type of measurand. Usually, piezoelectric sensing is accompanied by both mechanical displacement and electrical field. Thus, both the electrical and mechanical properties of the environment can be monitored directly by piezoelectric sensors. One may increase the number of measurands detected by the acoustic sensor by attaching or connecting a specific sensing element to a piezoelectric transducer/substrate. In this paper, piezoelectric sensing mechanisms and a wide range of bulk piezoelectric waves used in the sensor development are described. Applications of piezoelectric sensors in the chemical, environmental, medical, automotive, and aeronautic industries are also provided.