A flutter investigation has been made in the Langley transonic blowdown tunnel at Mach numbers between 0.79 and 1.34 on a thin 10 degree sweptback wing having an aspect ratio of 4 and a taper ratio of 0.6. The data obtained have been compared with data from NACA Research Memorandum L55I13A for zero and 30 degree sweptback wings of the type investigated, the flutter boundary for the 10 degree sweptback wing falls between those for the zero degree and 30 degree sweptback wings in the low supersonic Mach number range. However, the subsonic level (around a Mach number of 0.8) of the flutter boundary for the 10 degree sweptback wing lies above those for the zero and 30 degree sweptback wings. In addition, the amount of rise in the flutter boundary from the subsonic level to the supersonic values is about the same for the wings with angles of sweepback of 10 degrees and zero degrees, but is much greater for the wing with an angle of sweepback of 30 degrees.