Abstract : This thesis describes the construction of a Mach-Zehnder atom interferometer using Lithium. This device is made of three diffraction gratings, made of laser standing waves, almost resonant with the first resonance transition of lithium atom. The diffraction process relies on Bragg diffraction thus allowing only one diffracted order. It is elastic, i.e. only the atomic momentum is modified, leaving the kinetic energy and the internal state unchanged. Owing to an accurate collimation of the atomic beam, the two interfering atomic paths are spatially separated, so that one will be able to introduce a perturbation on only one atomic path. The first interference patterns achieved with this apparatus are shown in this thesis. From these results, we expect a very high sensitivity of the phase measurements because the fringe contrast is high and the mean detected flux is rather large. In the first part of this thesis, an historical introduction presents the advances in atomic manipulation with light, and more precisely in atom interferometry. After a theoretical discussion of the principles involved in this interferometer, the experimental setup is described in details, with a special attention to the detector operation. Then, the experimental results are shown and analysed. Finally, three planned measurements are discussed: the measurement of the refractive index of a gas for atomic waves, the measurement of the static electric polarizability of Lithium and a test of the neutrality of Lithium atoms.