Microemulsions are currently considered either as hard-sphere-like systems or as oil and water bicontinuous media. In this paper we will show that most of the time the microemulsion structure is of an intermediate character. This problem is closely related to the existence of critical consolute points in the oil–water–surfactant phase diagram. The study of the dynamical properties of these systems aids a better understanding of structural features. Our discussion is based on recent experimental data obtained on water-in-oil systems from various techniques: light scattering, electrical conductivity, ultrasonic absorption and transient electrical birefringence. A tentative picture of the possible mechanisms leading to a structural inversion to oil-in-water systems is proposed.