Though historically, the solar system has been the principal area for testing theories of gravitation, we seem to be at the end of the golden age of solar-system tests (Reasenberg (1987)). The classical effects have now been measured within the limits of today's technology and further significant improvements cannot be expected in the near term. Future space-based experiments such as GPB, Gravity Probe B; LAGOS, Laser Gravitational-Wave Observatory in Space; and POINTS, the (proposed) Astrometric Optical Interferometer, await further technological as well as engineering developments and logistic (launch) support to deliver them to the laboratory of space.

Recent years have seen, however, ground-based gravitational experimentation undergo a resurgence, driven by new experimental capabilities and by new theoretical work. The question that was raised by Fischbach et. al. (1986) of a possible short-range gravity force, dubbed the “Fifth Force,” has been particularly important. Though the experiments that gave rise to this suggestion have, in retrospect, turned out to be less compelling than was originally thought, the gravitational physics community has been forced to recognize the possibility of a short-range gravitational interaction.

This suggestion lent itself to fairly straightforward testing and the experimental community responded with great enthusiasm and ingenuity. Now some five years later, though it appears that this quite plausible theoretical suggestion has been ruled out by experiments at the level which initially was suggested. Nevertheless it gave rise to a rather exciting period in gravitational physics.