The ability to accurately track hand movement provides new opportunities for human computer interaction (HCI). Many of today's commercial hand tracking devices based on gloves can be cumbersome and expensive. An approach that avoids these problems is to use computer vision to capture hand motion. We present a complete real-time hand tracking and 3-D modeling system based on a single camera. In our system, we extract feature points from a video stream of a hand to control a virtual hand model with 2-D global motion and 3-D local motion. The on screen model gives the user instant feedback on the estimated position of the hand. This visual feedback allows a user to compensate for the errors in tracking. The system is used for three example applications. The first application uses hand tracking and gestures to take on the role of the mouse. The second interacts with a 3D virtual environment using the 3D hand model. The last application is a virtual DJ system that is controlled by hand motion tracking and gestures.