The observation of damage after earthquakes has highlighted that out-of-plane failures of masonry infill walls are somewhat frequent. In many cases, the structure withstands the ground shaking with minor damage, whereas infills collapse in-plane or out-of-plane. Reducing seismic damage to these elements is of primary importance for different reasons, the first of which is to decrease casualty risk. Other reasons are the economic losses and the building remaining unusable. In this work, a state of the art review on the out-of-plane behaviour of masonry infill walls is presented. The study aims at identifying the main features affecting the out-of-plane resistance and ductility of infill panels. The review includes the results of many experimental tests. Moreover, different models proposed in the literature for the assessment of the out-of-plane response of masonry infills are discussed. It is concluded that the slenderness and the boundary conditions of the panel and the presence of cracks due to prior in-plane damage play a fundamental role. Finally, it is highlighted that some situations, like for example the presence of openings in the panel, have not been investigated adequately.