The book presents modern metallographic research methods - light and electron microscopy, fractography, X-ray diffraction and micro-X-ray spectral analyzes, high-temperature metallography. State diagrams of the most important titanium-based double and triple systems are given, as well as metastable diagrams illustrating the phase composition of double and triple titanium alloys after quenching from different temperatures. Much attention is paid to the relationship of mechanical and especially service properties with the phase state and microstructure parameters of titanium alloys. Typical macro- and microstructures of semi-finished products from industrial titanium alloys in various states, encountered defects and possible causes of their formation are given.