<p>Titanium its alloys are now among the most important engineering materials because of their unique combination of high specific strength, low density, excellent corrosion resistance, biocompatibility, and superior performance at elevated temperatures. The review is a complete and unified study on the metallurgy, classification, mechanical properties and industrial applications of titanium alloys, with particular emphasis on their weldability using modern and advanced joining processes. Titanium has an allotropic transformation from the hexagonal close-packed (hcp) α-phase to the body-centered cubic (bcc) β-phase at ~ 882&#xa0;°C. This transformation lays the structural foundation for the classification of titanium alloys into four main categories: commercially pure titanium (CP-Ti), α and near-α alloys, α + β alloys, and β alloys—each offering a different combination of strength, ductility and heat-treatability. The main welding processes considered are gas tungsten arc welding (TIG/GTAW), laser beam welding (LBW), electron beam welding (EBW), and friction stir welding (FSW). A systematic review of the effect of these processes on microstructure, hardness, tensile strength, fatigue life and heat-affected zone (HAZ) characteristics for both similar and dissimilar metal joints is presented. Particular attention is paid to the problems of high chemical activity of titanium to oxygen and nitrogen in the welding process, the use of protective gases and activated fluxes, and the use of post-weld heat treatment (PWHT) to improve mechanical performance. The review further underlines important knowledge gaps especially for the welding of pure α- and β-titanium alloys and indicates the growing significance of hybrid welding techniques and interlayer-assisted dissimilar joining.</p> Graphical abstract <p></p>