Abstract: An improved device for stabilizing and stiffening an extension ladder includes a telescoping member with proximal and distal ends, a base that is attached to the proximal end of the telescoping member and has a configuration which is adapted to allow it to be adjustably affixed between the rungs of the ladder so that the angle between the centerline of the telescoping member and the plane defined by the extension ladder's rungs can be adjustably set so that the distal end of the telescoping member extends approximately horizontal to contact the vertical surface against which the extension ladder is leaning, and a transverse member that is attached to the telescoping member's distal end and has a configuration which is adapted to enhance the ability of the ladder to resist twisting about the centerline of the ladder.