Abstract: The extensible truck bed platform comprises a liner and a sliding bed for a pickup truck. The sliding bed may slide rearward on rails when the truck's tailgate is down to ease the task of loading and unlocking the truck bed. The liner fits into and couples to the cargo bed of the pickup truck. The liner covers the floor, side walls, and front wall of the bed. The sliding bed slidably couples to the liner via rail guides located on the liner and rails located on the sliding bed. The placement and spacing of the guide and rails in combination with overhangs on both the guides and rails prevent the sliding bed from moving in vertically or laterally relative to the liner but allows forward and backward movement of the sliding bed.