Among different methods used for the measurement of interfacial tension, the pendant drop is particularly well adapted to liquid-liquid interfaces. Using an integrated form of Laplace’s equation, we have developed an automatic pendant drop tensiometer which allows a real-time measurement (i.e., three to five measurements per second) with an accuracy less than 0.1%. The very new feature of this tensiometer is the possibility of controlling the interfacial area and the interfacial tension during an experiment for the study of (i) adsorption processes at constant area or tension and (ii) the dynamical properties of the Marangoni effect for adsorbed layers.