Augmented Reality (AR) is implemented by superimposing virtual entities on the real scene so that they appear registered with the related real entities. For the registration to be reliable, qualified object tracking technologies are necessary. In this talk, we address the problems of 3D object tracking in implementing practical AR systems: handling multiple 3D objects, motion blur, and texture-less objects. Presenting the solutions for these problems, we focus on reducing the tracking dependency on the complex texture. Finally, in the texture-less object tracking, we show how to exploit the depth information obtained in real-time using Microsoft Kinect.