This book presents a practical guide to the analysis of materials and includes a thorough description of the underlying theories and instrumental aberrations caused by real experiments. The main emphasis concerns the analysis of thin films and multilayers, primarily semiconductors, although the techniques are very general. Semiconductors can be very perfect composite crystals and therefore their study can lead to the largest volume of information, since X-ray scattering can assess the deviation from perfection.The description is intentionally conceptual so that the reader can grasp the real processes involved. In this way the analysis becomes significantly easier, making the reader aware of misleading artifacts and assisting in the determination of a more complete and reliable analysis. The theory of scattering is very important and is covered in such a way that the assumptions are clear. Greatest emphasis is placed on the dynamical diffraction theory including new developments extending its applicability to reciprocal space mapping and modelling samples with relaxed and distorted interfaces.A practical guide to the measurement of diffraction patterns, including the smearing effects introduced to the measurement, is also presented.