What Determines the Nature of Gravity? A Phenomenological Approach

The gravitational field can only be explored through the motion of test objects. To achieve this one first has to set up the correct equations of motion. Initially these equations are based on Newton's laws. Corresponding experiments that support Newton's laws are described. Furthermore, the basic characteristics of the motion of test objects in gravitational fields are described. This leads to the notion of Einstein's Equivalence Principle which has as consequence a metric theory of gravity. One particular metric theory is General Relativity based on Einstein's field equations with its particular predictions for effects like periastron advance, light deflection, etc. An overview over the experimental confirmation of General Relativity, in particular those presented at this workshop, is given. This workshop summary ends with open problems. We also describe some of the strategies for the experimental search for a quantum gravity theory.