The history of gravity measurements begun in 1604 with Galileo Galilei experiments on the acceleration due to the gravity force of the earth, g, along inclined planes. In his memory, the most used unit to measure g is the gal (10？2？m/s2). The paper takes the interested reader through a walk along some of the most important achievements in gravity measurements and gives some perspectives for future developments in terrestrial gravity. 1. Introduction The gravity force of the earth is a physical quantity of interest for geodesy, geophysics, and metrology. It is the main force which is responsible of the structure and shape of the earth. The combined effect of gravitational attraction and centrifugal force acts to distribute less dense material in the outermost layers of the earth and denser one in the innermost ones. The study of the shape of the earth and of its deformation is the basic topic of geodesy. To describe the shape of the earth, geodesists have chosen the equipotential surface which coincides with the surface of the mean sea level in a given epoch, the geoid. The surface of the mean sea level in a given epoch is determined by the gravity field of the earth. From the gravity field it is possible to determine the morphology of the geoid over the entire planet. Space geodesy and in particular satellite altimetry provides a direct measurement of the sea level surface over the oceans and hence the determination of the geoid. The determination of the geoid over the land is, however, possible only by means of the gravity field. The geoid is the reference surface for elevation measurements and it is therefore important for both cartography and navigation purposes. Oceanic currents are also partly controlled by the morphology of the geoid and hence a knowledge of the geoid is of importance for oceanography, hydrology, and for environmental studies related with possible changes of the mean sea level. Geophysics is more concerned with studying anomalies in the gravity field which are due to anomalous distribution of masses within the earth. Geodynamical processes like plate tectonics, mountain building, convective motions in the earth mantle, and volcanism have all strongly changed the mass distribution within the earth from that which would have been produced simply by the combined effects of gravitational attraction and centrifugal force. The thickness and composition of the earth lithosphere are highly variable over the whole planet. This diversification generates important anomalies in the gravity field. Geophysics is particularly interested in the
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