A leaf seal for effecting a seal between two, coaxial, relatively rotating components. The leaf seal has an annular pack of stacked leaves. The pack is mountable to a first one of the components with interleaf gaps formed between working portions of neighbouring leaves. The leaves extend towards the other component such that end edges of leaf working portions are presented for wiping contact with the other component. At least adjacent its end leaf edge, each leaf has a rear section at or adjacent the low pressure side of the pack and a front section which extends from the rear section to the high pressure side of the pack. The rear sections of the leaves are thicker than their respective front sections to reduce the interleaf gaps at the rear sections such that most of the pressure drop across the pack is over the rear sections.