Many processes in biotechnology (e.g., gas supply for fermentation vessels) and in process engineering (e.g., foaming with membranes) require the knowledge of how bubbles are formed at pores and at porous plates. Bubble build-up at and release from the pores are both complex processes due to the constant change in bubble size, shape, and compressibility. The relevant literature to these processes is summarized here, and the bubble formation and bubble release processes in stationary and moving media are described. The factors that influence bubble formation and movement are deduced from the forces that act on a forming bubble. Empirical approaches from the literature are presented, which estimate the bubble size in dependence of the process parameters. Bubble formation depends on the one hand on the gas flow through the pores, on the other hand one has to distinguish between bubble formation in stationary and in moving media.