We present the first direct measurement of the gravity-field curvature based on three conjugated atom interferometers. Three atomic clouds launched in the vertical direction are simultaneously interrogated by the same atom interferometry sequence and used to probe the gravity field at three equally spaced positions. The vertical component of the gravity-field curvature generated by nearby source masses is measured from the difference between adjacent gravity gradient values. Curvature measurements are of interest in geodesy studies and for the validation of gravitational models of the surrounding environment. The possibility of using such a scheme for a new determination of the Newtonian constant of gravity is also discussed.In the last two decades, atom interferometry [1] has profoundly changed precision inertial sensing, leading to major advances in metrology and fundamental and applied physics. The outstanding stability and accuracy levels [2,3] combined with the possibility of easily implementing new measurement schemes [4][5][6][7] are the main reasons for the rapid progress of these instruments. Matter-wave interferometry has been successfully used to measure local gravity [8], gravity gradient [9-11], the Sagnac effect [12], the Newtonian gravitational constant [13][14][15][16], the fine structure constant [17], and for tests of general relativity [18,19]. Accelerometers based on atom interferometry have been developed for many practical applications including geodesy, geophysics, engineering prospecting, and inertial navigation [20][21][22]. Instruments for space-based research are being conceived for different applications ranging from weak equivalence principle tests and gravitational-wave detection to geodesy [23,24].One of the most attractive features of atom interferometry sensors is the ability to perform differential acceleration measurements by simultaneously interrogating two separated atomic clouds with high rejection of common-mode vibration noise, as demonstrated in gravity gradiometry applications [3,9]. In principle, such a scheme can be extended to an arbitrary number of samples, thus, providing a measurement of higher-order spatial derivatives of the gravity field. Geophysical models of the Earth's interior rely on the inversion of gravity and gravity gradient data collected at or above the surface [25]. The solution to this problem, which is, in general, not unique, leads to images of the subsurface mass distribution over different scale lengths [26]. In this context,