A method of processing a primitive in a graphics processing system, the method comprising tiling the primitive to determine which of a plurality of tiles of a rendering space the primitive at least partially overlaps with, and rendering the primitive in said tiles, wherein said tiling the primitive comprises: determining a bounding box for the primitive; for each of at least one tile boundary (1104, 1114, 1124) between lines of tiles in the bounding box, determining intersection points (1108 2, 1108 3, 1118 2, 1118 3) of the tile boundary with edges of the primitive, wherein the lines of tiles are rows or columns of tiles; and using the determined intersection points to determine which of the tiles in the bounding box the primitive at least partially overlaps with, wherein said determining intersection points of the tile boundary with edges of the primitive comprises: for each edge of the primitive, unless it is parallel to the tile boundary, determining an initial intersection point (1108 1, 1108 2, 1108 3, 1118 1, 1118 2, 1118 3) of the tile boundary with an edge line (1106, 1116), wherein the edge line is represented by a line equation, and wherein the edge lines define the edges of the primitive; and identifying which of those initial intersection points lie on the edge of the primitive, wherein the identified initial intersection points are the determined intersection points (1108 2, 1108 3, 1118 2, 1118 3) which are used to determine which of the tiles in the bounding box the primitive at least partially overlaps with. determining a bounding box for the primitive; for each of at least one tile boundary (1104, 1114, 1124) between lines of tiles in the bounding box, determining intersection points (1108 2, 1108 3, 1118 2, 1118 3) of the tile boundary with edges of the primitive, wherein the lines of tiles are rows or columns of tiles; and using the determined intersection points to determine which of the tiles in the bounding box the primitive at least partially overlaps with, wherein said determining intersection points of the tile boundary with edges of the primitive comprises: for each edge of the primitive, unless it is parallel to the tile boundary, determining an initial intersection point (1108 1, 1108 2, 1108 3, 1118 1, 1118 2, 1118 3) of the tile boundary with an edge line (1106, 1116), wherein the edge line is represented by a line equation, and wherein the edge lines define the edges of the primitive; and identifying which of those initial intersection points lie on the edge of the primitive, wherein the identified initial intersection points are the determined intersection points (1108 2, 1108 3, 1118 2, 1118 3) which are used to determine which of the tiles in the bounding box the primitive at least partially overlaps with. for each edge of the primitive, unless it is parallel to the tile boundary, determining an initial intersection point (1108 1, 1108 2, 1108 3, 1118 1, 1118 2, 1118 3) of the tile boundary with an edge line (1106, 1116), wherein the edge line is represented by a line equation, and wherein the edge lines define the edges of the primitive; and identifying which of those initial intersection points lie on the edge of the primitive, wherein the identified initial intersection points are the determined intersection points (1108 2, 1108 3, 1118 2, 1118 3) which are used to determine which of the tiles in the bounding box the primitive at least partially overlaps with.