After-Shadow: a Friendly Platform for Social Interactions In large buildings, apartments or on campus, we often encounter people living in the same space as we wait for the elevator or walk down the corridor, but due to different work schedules, distance or other factors, we may not know each other. We should call this relationship “familiar strangers”. The main purpose of this project is to explore a new type of interpersonal communication model founded upon digital media, interactive technology and environment perception devices, where it functions as a medium that is natural and genuine for the amelioration of interpersonal interactions, bonding familiar strangers in everyday life. The device used in this project will be installed in elevators and corridors. When people are waiting for the elevator or crossing the corridor, a “shadow” will be temporarily produced and various “dance” gestures generated through digital image processing technology, gently incorporating object contours in a virtual scene. With changes over time and different “shadows” joining and leaving, virtual interactions allow familiar strangers to connect their lives together, making it a fun and effective interaction channel. The research and design of this system can be used not only to convey messages in social interaction contexts or in environment navigation, but also for interactive games or physical performances, thereby enhancing the creative added-value of digital technology application.