Abstract: A flange wrench for tightening and loosening pipe flanges onto/off of pipes has a drive head and an elongate handle. The drive head has a flat planar surface essentially parallel to a longitudinal axis of the wrench handle, and a pin extending therefrom essentially normal to the plane of the essentially planar surface. The head also includes a first essentially planar shoulder surface that is adjacent to and generally normal to the first planar mating surface, such that the planar shoulder surface is generally parallel to the axis of the pin. To use the flange wrench, the user inserts the pin into an existing or drilled mounting hole in the flange and positions the wrench planar mating surface against the planar surface of the flange such that the flange wrench planar shoulder surface is adjacent the circumferential edge of the flange.