Atom Interferometers rely on the wave properties of matter which govern the scattering of neutral atoms from obstacles (gratings). We have developed two kinds of atom interferometers that operate entirely in the time domain using a cloud of cold (100 micro kelvin) atoms. Atom optical elements such as gratings and beam splitters involve pulsed laser fields which are used to manipulate atoms in their ground states. The consequence of diffraction of matter waves from (light) gratings is the formation of atomic gratings. These gratings have a spatial periodicity of the order of the wavelength of light. We have used the properties of atomic gratings to make sensitive measurements of the discrete nature of atomic recoil, gravitational acceleration, velocity distributions, magnetic fields, and collision cross sections. Other applications include atom lithography.