Coalbed methane (CBM), once a hazard to the undermining safety, is becoming an important addition to the global energy supply. Injecting carbon dioxide \((\hbox {CO}_{2})\) into coal seams not only aids to enhance CBM production but also offers an option of \(\hbox {CO}_{2}\) sequestration helpful for the reduction of greenhouse gas release. Multiphase flow occurs in those cases as most coalbeds are initially saturated with water. Accurate determination of relative permeability of coal plays an important role in the prediction and evaluation of those operations because it is in effect the effective permeability (absolute permeability multiplied by relative permeability) to gas/water rather than absolute permeability that controls the flow in coal seams. To date, varying methods have been reported of obtaining relative permeability curves of coals through either laboratory tests or field data analysis, which are reviewed in this paper. Also, this paper includes a summary of the characteristics of relative permeability curves of coals, relative permeability models, effects of varying factors on curves and effects of the curves on CBM production. This paper concludes that despite the importance of relative permeability in CBM-related operation process, limited research efforts have been paid on improvements concerning this subject in the past two decades: the advance in the research of relative permeability-related subjects can barely keep up with the rate at which the developments of CBM and \(\hbox {CO}_{2}\)-ECBM projects are booming worldwide. More efforts are needed to conduct related investigations such that a reliable standard or workflow can be established that can as accurately determine coal relative permeability with repeatability.