Bragg diffraction occurs when radiation of a wavelength  comparable to atomic spacings is scattered in a specular fashion (mirror-like reflection) by planes of atoms in a crystalline material, and undergoes constructive interference. When the scattered waves are incident at a specific angle, they remain in phase and constructively interfere. The glancing angle  (see figure on the right, and note that this differs from the convention in Snells law where  is measured from the surface normal), the wavelength , and the "grating constant"  of the crystal are connected by the relation:where  is the diffraction order ( is first order,   is second order,  is third order). This equation, Braggs law, describes the condition on θ for constructive interference.
A map of the intensities of the scattered waves as a function of their angle is called a diffraction pattern. Strong intensities known as Bragg peaks are obtained in the diffraction pattern when the scattering angles satisfy Bragg condition. This is a special case of the more general Laue equations, and the Laue equations can be shown to reduce to the Bragg condition with additional assumptions.