A window ledge support system, in particular a window sill support system, comprising a window ledge support unit containing a front side, a rear side and an upper side and a first side boundary of the upper side, and if appropriate, an, in particular opposite, second side boundary of the upper side, wherein the upper side in the case of the generic use of the window ledge support unit has or forms a run-off surface that slopes downwards in a direction from the rear side towards the front side; a first window ledge profile in the area of the first side boundary of the upper side, wherein the first window ledge profile is essentially L-shaped with a first leg comprising a lower side, which in case of the generic use of the window ledge support system is essentially vertically oriented, and a second leg, which is essentially horizontally oriented, and which has an extension in the direction of a second window ledge profile which has an extension in the direction of a possibly opposite second window ledge profile, and comprising one first window ledge slide profile, wherein the first window ledge slide profile is a first plaster removal profile and is designed and configured for connection with the first window ledge profile, containing a reinforcement fabric, and if appropriate, a second window ledge profile in the area of the second side boundary of the upper side, wherein the second window ledge profile is essentially L-shaped with a first leg comprising a lower side, which in case of the generic use of the window ledge support system is essentially vertically oriented, and a second leg, which is essentially horizontally oriented, and which has an extension in the direction of a second window ledge profile, and comprising a second window ledge slide profile, wherein the second window ledge slide profile is a second plaster removal profile, designed and configured for connection with the second window ledge profile, preferably containing a reinforcement fabric; a supporting area for a profile frame, in particular a window or door frame, which is connected on the rear side to the upper side of the window ledge support unit; and at least one first watertight layer comprising a rearward edge, in particular foil, at or on the upper side of the window ledge support unit and at least in sections at or on the supporting area (also known as the first embodiment); or at least one second watertight layer comprising a rearward edge, in particular foil, at or on the upper side of the window ledge support unit and at least one third watertight layer comprising a front edge, in particular foil, at least in sections at or on the supporting area, which with the second watertight layer forms an overlapping area such that in case of the generic use of the window ledge support system, the rearward edge of the second watertight layer is present below the front edge of the third watertight layer, in particular is sealed therewith (also known as the second embodiment); or at least one fourth watertight layer, in particular foil, comprising a rearward edge, with a first section at or on the upper side of the window ledge support unit and an adjoining rearward second section configured and designed for the, in particular adhesive, placement on a profile frame (also known as the third embodiment).