Abstract: A tractor drawn and powered impeller mower-conditioner includes a transverse cutter assembly comprising a series of side-by-side rotating cutting disks. An impeller rotor with free-swinging flails is mounted above and slightly to the rear of the cutter bar with its axis of rotation parallel to the cutter assembly. A hood over the rotor includes a confining forward conditioning plate conforming fairly closely to the rotor periphery to form a conditioning zone and a rearwardly extending deflecting and windrow forming portion. The rotor is disposed and rotated so that the flails intercept cut material delivered rearwardly by the cutter assembly and carry it inside the hood up and over the rotor through the conditioning zone to be discharged rearwardly into a windrow.