This review is presented as a part of the literature review performed in the Clean Sky project LEAN - Development of light-weight steel castings for efficient aircraft engines, coordinated by Swerea SWECAST during 2011-2013. From a foundryman’s point of view, fluidity is related to the ability for a metal to fill a mould while fluidity is related to viscosity in physics. A distinction is made between flowability and fillability depending on which mechanism is reducing the ability to flow. Fillability is related to flow problems when surface tension is the governing mechanism and flowability is related to heat transfer. The influence of surface tension will be more important as the thickness of the casting is decreased whereas heat transfer has a more pronounced influence on thicker sections, but still thin. Several parameters related to both the process and alloy affect the ability to fill a thin section. Increasing super heat, mould temperature or pressure head will improve fluidity. Changes in alloy composition will also to some extent have impact on fluidity. Flow rate and shell permeability is also important parameters. There are also other possibilities that can improve fluidity. Vacuum-assisted casting is one method which has been proven effective. This method is used both for gravity and counter gravity casting. Vibrating is yet an other method which improves fluidity.