The invention provides for a roofing membrane tensioner 10 having a base 102 with a hook 36 for catching the edge 22 of an underlying surface 20, a membrane connector 108, and a means for moving the membrane connector towards the edge by applying force inwardly 24 from the edge. The means for moving the membrane connector towards the edge can be a lever 104 operated substantially in the same plane as the underlying surface. The force can be applied at least 50 cm from the edge. The base can have a flat side and a hook side. The base can also have a mount 110 for connecting the lever. The mount can be the fulcrum 110 for the lever.The invention also provides for a method for tensioning a roof membrane 40 towards an edge 22 of a roof surface 20 by securing a preceding tab 41 of the roof membrane to the roof surface, hooking a slidable base 102 having a fulcrum 110 for an attached lever 104 to the edge, connecting a membrane connector 108 between a subsequent tab of the roof membrane and the lever on one side of the fulcrum, and tensioning the roof membrane by applying inwardly 24 directed effort to the lever on the other side of the fulcrum.The invention also provides for a roof membrane tensioning system 10 having a mounting means for positioning and adjusting a base 102 on a roof 20, a membrane connector 108, and a membrane tensioning mechanism for tightening the membrane towards an edge of a roof by applying force inwardly 24 from the edge 22.