The present invention relates to a deployment handle for a prosthesis delivery device and to a delivery device including such a handle. The handle assembly facilitates the controlled release of a prosthesis from the delivery device, while ensuring that various deployment steps are performed in a particular sequential order. The handle assembly comprises a main handle and a second handle which is rotatably and/or longitudinally moveable relative to the main handle. The second handle has an initial position on the main handle such that it prevents access to, and premature manipulation of, a proximal stent release mechanism, until the stent graft has been at least partially unsheathed.