[en] This study deals with the contribution that space measurements can make to understanding the nature of one of the four fundamental forces in the universe--gravitation. Studies in fundamental physics are being carried in earthbound laboratories, often involving the highest-energy accelerators, but the force of gravity is so weak in comparison with the other forces that only space provides an environment sufficiently free from perturbations to make possible the extra-ordinarily sensitive measurements described in this report. Gravitational experiments performed to measure relativistic effects have been limited mainly to observing the behavior of clocks, light rays, and test particles under the influence of massive bodies like the sun and Earth. The proposed strategy involves a broadening of these experiments through measurements in space of entirely new phenomena, extension of previous measurements to substantially higher levels of accuracy, and improvements of instrumentation to attempt to detect gravitational waves. Recommendations for experiments in the 1980's are divided into two classes, based on cost. The first class involves experiments that either require a dedicated spacecraft or have a major impact on a spacecraft; the second class contains experiments that either rely solely on ground-based measurements or represent small additions to spacecraft devoted primarily to other goals