Abstract:Liquid foam is a typical non-equilibrium complex system withhierarchy and self-organization structure. The process by which liquid fromboth films and Plateau borders drains out of a freshly made foam as a resultof the gravitational force and the capillary force is called foam drainage,which plays a vital role in foam stability. From the view of foam physics,this paper firstly gives a brief introduction to the regular foamstructure, and then explains three main mechanisms for foams to evolveinto equilibrium state, drainage, gas diffusion and film rupture. Thedifferences and similarities between foam-like materials and porous mediaare discussed. Recent progress in studies on foamdrainage is reviewed, including of the treatment of boundarycondition of Plateau border and the corresponding flow regimes, drainagemodels and applications in one dimensional foams, and the results in 2D foamdrainage. We also discuss techniques used in foams drainage experimentsand the recent important progress in the experimental and theoreticalstudies on foam drainage in space.