The present monograph is not a self-contained introductory text. Instead it presupposes to a large extent that the reader is not only thoroughly familiar with the special theory of relativity, but that he or she has studied the standard aspects of the general theory, as weIl. Starting from local and global formulations of the principlcs of inertia and relativity, we discuss the microscopic ancl telcscopic aspects of gravitation. Our central goal has been to demonstrate that the foundations of gravitational theory laid by Newton and Einstein imply questions on thc relation betwecn the micro-...