Analytical methods for the nondestructive characterization of thin epitaxial films, multilayers and superlattices by x-ray diffraction that have been developed in the last decade are reviewed in three sections: 1. I. Description of the strain state by the strain tensor and determination of homogeneous strains and stresses by double-crystal diffractometry in Bragg case reflection; 2. II. Determination of inhomogeneous strains, such as strain gradients or periodic strain modulations, by double-crystal diffractometry in Bragg case reflection; 3. III. Characterization parallel to the surface by grazing-incidence x-ray diffraction. © 1989.