Leaf seals are a new evolving sealing technology for air to air sealing locations within gas turbine engines. They have sealing characteristics similar to a brush seal, while not suering from the degradation seen by these. An extensive investigation into leaf seals has been carried out and is discussed herein. With the gained understanding of the leaf seal and the developed modelling capabilities it is possible to establish the leaf seal as a new high performance sealing alternative for gas and steam turbines.