The invention relates to an input device in the form of a single-hand keyboard, comprising a substantially flat housing (1) approximately in the shape of a quadrant of a circle, in which housing a first keyboard circuit board having associated first keys (2) is accommodated, the first keys (2) lying on a first housing side (3) and being arranged along concentric circular arc segments in the manner of a fan. A second keyboard circuit board having associated second keys (4) is accommodated in the housing (1), the second keys lying on the second housing side (5) facing away from the first housing side (3), and the layout of the second keys (4) being mirror-inverted with respect to the layout of the first keys (2). Furthermore, a detection element for determining the current orientation of the input device is provided in the housing (1). The detection element activates only the keyboard circuit board facing upward and deactivates the other keyboard circuit board, depending on the orientation.