Acoustic measurement techniques are being developed to monitor the state of equipment and the physicochemical changes within chemical engineering processes. The advantage of acoustics is that unlike other techniques, direct contact with the process under investigation is not required so intrusion can be kept to a minimum. Most research concentrates on the active use of low-powered ultrasound, i.e, the generation of an acoustic wave and the measurement of any changes in the wave, This review highlights the use of passive measurement of acoustic emissions created by a process as a potentially non-invasive, real-time monitoring technique to be used in process control. Research into the acoustic emission sources found in several chemical engineering processes such as gas-liquid mixing, solid systems and chemical reactions and the process information that can be obtained from them is discussed.