In an first aspect, a ladder for mounting on a vehicle trailer includes an attachment bracket assembly for mounting on the trailer; a first side rail; a second side rail parallel to the first side rail; and a plurality of rungs pivotally connected to both the first and second side rails. The ladder is collapsible to decrease a distance between the first and second side rails. In a second aspect, a ladder for mounting on a vehicle trailer includes an attachment bracket; a first side rail; a second side rail parallel to the first side rail; a plurality of rungs connecting the first and second side rails; and a pivotal connection. The first and second side rails define a plane and the pivotal connection allows for rotation of the plane about a vertical axis. The pivotal connection is disposed between the attachment bracket and the first side rail.