Abstract: A portable single-sided armrest assembly that is added to or removed from any seating device/location without requiring any fixed mounting or permanent or semi-permanent attachment means. The armrest assembly includes an L-shaped member having a lower plate section serving as a seat for the person using the armrest while further including a backplate section which slidably mounts an upright support plate or portion. One end of the support plate includes an elongated cushion armrest fixedly attached thereto, while further including an elongated slot mounting a threaded cap serving as a guide as the support plate is moved to a desired vertical position. A lock knob is employed for securing the armrest and support plate in a fixed location on the backplate. An adapter plate is employed for attachment between an angular section joining the backplate of the L-shaped member to the lower seat section of the member, wherein the adapter is employed to occupy a vacant right angled space in a standard seat.