An example information processing system includes a main unit, a first controller device and a second controller device. The main unit includes a display. The first controller device is configured to be removably attached to the main unit, and the first controller device transmits first operation data representing an operation performed on the first controller device to the main unit, irrespective of whether the first controller device is attached to the main unit. The second controller device is configured to be removably attached to the main unit, and the second controller device transmits second operation data representing an operation performed on the second controller device to the main unit, irrespective of whether the second controller device is attached to the main unit. The main unit displays, on the display, an execution result of an information process based on the first and the second operation data.