Void fraction measuring techniques are reviewed with emphasis on applications to multiphase flow. The presentation is divided into two main sections; intrusive where the probe penetrates into the flow field, and non-intrusive where the detection is done remotely. The latter is more preferrable than the former. We subdivided the non-intrusive techniques into into two main categories; nuclear and non-nuclear. In the nuclear section, we discussed the utilization of almost all types of radiations, namely; beta, neutrons, gamma, X-ray, near infrared, in addition to the nuclear magnetic resonance. In the non-nuclear techniques, we presented the following methods; fluorescence, optical sensors, laser, autotransformer winding, ultrasonic, and photgraphy. Some other non nuclear miscellaneous techniques were discussed.