A gas turbine engine comprising: a circumferential array of airfoils, each of said airfoils including a platform defining a radial boundary of a working fluid flow path, and wherein said airfoils comprise turbine blades with said platforms of adjacent turbine blades being spaced from each other by a gap; said platform including a first major surface exposed to a flow of working fluid and a second major surface defining at least in part, a cavity containing cooling air; the platforms of adjacent airfoils being engaged by a seal spanning said gap and which bears against said second major surfaces of said platforms across a first major surface of said seal and is exposed to said cooling air across a second major surface of said seal, first and second end portions (100, 105) seating against fore and aft ends of the cavity; said second major surfaces of said platforms and said first major surface of said seal defining at least one cooling air passage therebetween which establishes a flow of said cooling air through said cooling air passage, thereby enhancing the convective cooling of said platform; characterised in that: said cooling air passage comprising a plurality of grooves in said second major surface of said platform and in said first major surface of said seal such that said cooling fluid enters said cooling air passage from an end thereof and traverses said passage between said seal and said platform and exhausts along said first major surface of said seal between said adjacent platforms, said seal includes at least one of a concave or convex portion formed along at least one of its longitudinal side edges, said at least one concave or convex portion spanning multiple grooves formed in said first major surface of said seal. a circumferential array of airfoils, each of said airfoils including a platform defining a radial boundary of a working fluid flow path, and wherein said airfoils comprise turbine blades with said platforms of adjacent turbine blades being spaced from each other by a gap; said platform including a first major surface exposed to a flow of working fluid and a second major surface defining at least in part, a cavity containing cooling air; the platforms of adjacent airfoils being engaged by a seal spanning said gap and which bears against said second major surfaces of said platforms across a first major surface of said seal and is exposed to said cooling air across a second major surface of said seal, first and second end portions (100, 105) seating against fore and aft ends of the cavity; said second major surfaces of said platforms and said first major surface of said seal defining at least one cooling air passage therebetween which establishes a flow of said cooling air through said cooling air passage, thereby enhancing the convective cooling of said platform; characterised in that: said cooling air passage comprising a plurality of grooves in said second major surface of said platform and in said first major surface of said seal such that said cooling fluid enters said cooling air passage from an end thereof and traverses said passage between said seal and said platform and exhausts along said first major surface of said seal between said adjacent platforms, said seal includes at least one of a concave or convex portion formed along at least one of its longitudinal side edges, said at least one concave or convex portion spanning multiple grooves formed in said first major surface of said seal.