The instrumentation aims at improving the implantation of a glenoidal prosthetic component which is both provided with a convex articular surface defining a joint axis and intended to articulate with a humeral prosthetic component, and which is adapted so as to be fixedly assembled with a plate to be anchored to the glenoid, the assembly between the glenoidal prosthesis component and the plate being centered on an implantation axis which is both parallel and shifted relatively to the joint axis, the relative position of the glenoidal prosthesis component and of the plate being adjustable around the implantation axis before fixing the assembly. The instrumentation comprises a tool for positioning the glenoidal prosthetic component and the plate relatively to each other angularly around the implantation axis, this tool comprising a body, which, in use, extends transversely to the implantation axis and which is provided with localization elements for localizing an implantation angle centered on the implantation axis, so that the tool is able to intra-operatively protract the implantation angle with respect to the glenoid.
