A gesture language for a device with multiple touch surfaces is described. Generally, a series of new touch input models is described that includes touch input interactions on two disjoint touch-sensitive surfaces. For example, a mobile device can include a primary display on a “front” side of the device, and a secondary display or touch-sensitive surface on the “back” side of the device, such as a surface that is opposite the primary display. Accordingly, the gesture language can include a series of “back touch” interactions with the touch-sensitive surface on the backside of the device. Example interactions include direct and indirect touch input on the back side, as well as simultaneous touch input on both sides of the device.