Diffraction gratings were discovered at the 18 th century and they are now widely used in spectrometry analysis with outstanding achievements spanning from the probing of single molecules in biological samples to the analysis of solar systems in astronomy. The fabrication of high quality diffraction gratings requires a precise control of the period at a nanometer scale. The discovery of lasers in the 1960's gave birth to the optical beam lithography in the 1970's. This technology revolutionized the fabrication of diffraction gratings by offering a highly precise control of the grating period over very large scales. It is surprising to see that a few years after, the unique spectral properties of diffraction gratings revolutionized in turn the field of high energy lasers. We review in this paper the physics of diffraction gratings and detail their interest for the pulse compression of high power laser systems. Light diffraction is a fundamental and emblematic problem in optics. Diffraction gratings are optical components of major importance in the spectral analysis of light. They consist of a periodic modulation at the wavelength scale of an interface between two or more materials (see Fig.1). Their unique spectral properties rely on the fact that the light impinging on the periodically modulated surface is reflected or transmitted in specific angles only, which is not the case if the modulation is aperiodic. The angles of propagation can be predicted by a very simple expression, the so-called grating's law, that can take the simple form: sin θ m + sin θ i = mλ /d. (1) in which d denotes the grating period, λ denotes the wavelength, θ m and θ i denote respectively the angles between the diffracted angles, the incident angle and the normal to the surface. m is a relative integer denoting the diffraction order. When m = 0 (classically called specular order), the diffraction grating does not exhibit spectral properties and acts as a mirror. Diffraction properties appear when m = 0 and it can be observed that in this case, the angle of diffraction θ m depends on the wavelength. This property is at the heart of the spectral analysis since plane-waves of different frequencies will not propagate in the same 1