A cutting insert having a generally polygonal insert body having a top face, a bottom face and a plurality of side walls extending therebetween. The juncture of each side wall with the top face defines a peripheral cutting edge. A chip breaking groove is formed in the top face and extends alongside the cutting edges. The chip breaking groove includes a descending wall which inclines downwardly from the cutting edges and a back wall which inclines upwardly from the rearward edge of the outside wall. The back wall includes a nose portion adjacent the cutting corner of the insert. The nose portion includes a tip and a pair of side edges which are disposed at an angle relative to the adjacent cutting edges of the insert body such that the width of the chip groove increases as it extends away from the cutting corner. A pair of shoulders are disposed on opposite sides of the nose portion and are disposed at an angle relative to the cutting edges of the insert body such that the width of the chip groove decreases as it extends from the cutting corner. In a preferred embodiment, the angle of inclination of the back wall relative to the top surface of the insert body increases as the back wall extends away from the cutting corner.