The year 2009 marks the 75^th anniversary of the discovery of X-ray interferences from lattice sources by Walther Kossel in the city of Gdansk. The X-ray source is located within the crystal itself and interferences (lattice source interferences) appear, whose evaluation provides information on a significant number of physical material parameters. For example lattice constants with a precision of 10⁻⁵ can be determined non-destructively in the micro-range. Moreover, both, the local lattice parameter and the local crystal structure, can be ascertained at low and high temperatures, which is important for the investigation of crystallographic lattice transformations and especially for the characterisation of superconductors (V₃Si). Beginning with the first Kossel investigations on copper single crystals in Gdansk up to computer simulated results on metals, intermetallic compounds as well as on complex materials, such as Cu-Sn phases (e.g., Cu₄₁Sn₁₁), with correspondingly running diffusion processes in microelectronical contacts, the Kossel technique provides comprehensive answers to current research questions. The article gives selected application examples from different fields. Moreover, the most important steps in the development of the Kossel interferences are briefly reviewed.