An inflatable lifejacket for providing buoyancy in water to a wearer of the lifejacket includes an inflatable buoyancy envelope which is donned by a wearer who passes his head through a neck opening in the envelope to bring a main body portion of the envelope to overlie the chest with a neck portion of the envelope passing round the sides and back of the neck and resting on the shoulders. The neck portion of the envelope is formed by two inflatable neck sections extending upwardly from the main body portion at each side thereof and at their upper ends being connected together in the region of the back of the neck of the wearer by constraining straps which hold the upper ends together in a manner which permits spacing of them when the envelope is uninflated to provide a neck opening through which the wearer can pass his head but which so constrains the two ends when the envelope is inflated as to define a neck opening which obstructs passage of the wearer's head. Additionally, the main body portion of the envelope is constrained in a region between its upper edge and its lower edge to reduce the radius of curvature of the envelope at its upper edge when the envelope is inflated.