The literature on the welding of titanium and its alloys is reviewed. Titanium is very reactive and is easily contaminated by carbon, hydrogen, oxygen or nitrogen. During welding, the hot metal must be protected at all times from the atmosphere, and it may be necessary to pay special attention to the purity of inert gases used for shielding. Commercially pure titanium and the alpha alloys are the most readily weldable, and have been considered as a group. The alpha-beta and beta alloys can be joined, but the welds tend to be brittle, and vary in their response to heat treatment. These alloys often need individual techniques and treatment to obtain optimum properties in the welded joints. The most useful fabrication methods are tungsten inert gas welding, metal inert-gas welding, and resistance spot and seam welding, and these have all been used extensively in aerospace applications. Good brazing methods have been developed and may be useful for "honeycomb" structures. Oth.er specialized methods, such as electron-beam welding and explosive welding, have been tried success fully. In the U.S.S.R. submerged arc welding and electro-slag welding are the most popular methods.