Abstract: An elastically deformable support for an expandable seal element of a downhole tool, an expandable seal assembly incorporating such a seal element and support, and a downhole tool, such as a packer, incorporating the expandable seal assembly are disclosed. The elastically deformable support may be one-piece. The support is deformable between an unexpanded configuration and a radially expanded configuration and includes a plurality of base portions, each base portion having a surface which, in use, faces towards the seal element; and a plurality of overlap portions, each overlap portion extending from a respective base portion so that it overlaps the surface of an adjacent base portion and having a surface which, in use, faces towards the seal element. The base portions and the overlap portions are arranged to define a generally ring-shaped seal support structure which forms a continuous circumferentially extending support surface for abutting and supporting the seal element.