In this paper we investigate the principles for desiging multifaceted displays and their potential interfaces. D20 is a prototype of a handheld digital device which has an icosahedron shape. Each face of the device is a triangular display, the entire surface of the device forms one continuous multisided display. The user interacts with the device by manipulating it. The principles that we develop can be applied to other non-rectilinear multifaceted displays. Keywords mobile and gestural interaction, multifaceted displays. ACM Classification Keywords H.5.2 [Information interfaces and presentations (e.g., HCI)]: User Interfaces---input devices and strategies, interaction styles, screen design; B.4.2 [Input/output and data communication]: Input/Output Devices--image display; C.5.3 [Computer system implementations]: Microcomputers---portable devices.