Double　skin　composite　columns　are　formed　from　two　steel　skins　filled　with　concrete　in　between.　This　new　form　of　hybrid　column　has　the　potential　to　be　used　in　many　domains　such　as　high-rise　bridge　piers　and　large　diameter　columns　in　high-rise　buildings,　etc.　This　paper　describes　a　series　of　tests　carried　out　on　concrete-filled　double　skin　steel　tubular　(CFDST)　stub　columns,　beams　and　beam-columns.　Both　outer　and　inner　tubes　are　cold-formed　rectangular　hollow　sections　(RHS).　The　failure　modes,　and　load-deformation　behaviour　of　CFDST　specimens　are　compared　with　those　of　conventional　concrete-filled　steel　tubular　members　and　empty　double　skin　tubular　members.　A　theoretical　model　is　developed　in　this　paper　for　the　CFDST　stub　columns,　beams　and　beam-columns.　Reasonably　good　agreement　is　observed　between　the　predicted　and　tested　curves.　Simplified　models　are　derived　to　predict　the　load-carrying　capacities　of　the　composite　members.　(c)　2005　Elsevier　Ltd.　All　rights　reserved.