In the application of advanced neuroscience techniques including optogenetics to small awake animals, it is often necessary to restrict the animal’s movements. A spherical treadmill is a beneficial option that enables virtual locomotion of body- or head-restrained small animals. Besides, it has a wide application range, including virtual reality experiments. This chapter describes the fundamentals of a spherical treadmill for researchers who want to start experiments with it. First, we describe the physical aspect of a spherical treadmill based on the simple mechanical analysis. Next, we explain the basics of data logging and preprocessing for behavioral analysis. We also provide simple computer programs that work for the purpose.