Atom interferometry exploits the fact that matter, like light, exhibits wave-like properties. In optical interferometry, light waves are recombined after propagating along different paths. Depending on the difference in the waves’ phase accumulated along the two paths, the light may interfere constructively and appear bright or it may interfere destructively and appear dark. Similar to an optical interferometer, an atom interferometer splits matter waves into different paths and recombines them in a coherent manner [1]. Cold-atom interferometry use atoms that are laser-cooled to millionths of a degree above absolute zero. The atom interferometer is then realized thanks to sequences of laser pulses used to split, deflect and recombine matter waves along different trajectories, acting as beam splitters and mirrors. Through measuring the resulting interference fringes, it is possible to extract the phase difference accumulated between the waves on the paths. Since these paths are influenced by inertial effects, inertial quantities that enter this phase difference can then be accurately determined, making atom interferometry a leading precision measurement technology with applications in both applied and basic science. Atom interferometers today are the most sensitive instruments for measuring gravity or accelerations, and probing fundamental physical phenomena. Future applications of cold-atom interferometry include inertial navigation, satellite gravimetry and space-based experiments to test gravity. These applications require a new generation of cold-atom interferometers capable of highly precise and stable measurements within compact configurations, and able to operate in real-world field conditions which represent a significant challenge for the community. This tutorial is designed to introduce those with a vague understanding of optical interferometers to cold-atom interferometry. We will outline the basic theory needed to calculate the observed phase shift, and indicate how this phase shift is experimentally determined. We illustrate the presentation with a description of some realizations of laboratory-based cold-atom sensors dedicated to fundamental tests of physics. Additionally, in the scope of both field and mobile applications, we will make a review of the progress made towards the development of such instruments for measuring gravitational and inertial signals and the possible benefits that cold-atom quantum sensing may offer in navigation. [1] Mark Kasevich and Steven Chu, Phys. Rev. Lett. 67 (1991), pp. 181–184.