This intriguing book examines the questions of how the ways in which we observe the world determine theories of physics and how we can get reliable results that enable us to make secure predictions. The first chapters deal with the theories of quantum mechanics and relativity and are followed by a discussion of chaotic dynamics. The uncertainty of observations and probabilistic agruments in physics are then treated. Finally, it is argued that the success of prediction is reason for believing in the existence of a world independent of ourselves.