Titanium alloys are well known as materials for high temperature applications, especially in aero engines where weight is very important. These alloys were used in early 1940. Today in XXI century due to the high specific strength, light weight, TiAl - based alloys find increasing applications as structural materials in advanced engineering structures, as a bio compatible material (hip prosthesis). Unfortunately TiAl based materials show quite poor resistance at high temperatures, above 600 oC in different environments (oxidation. Sulphidation, oxidation/sulphidation), thus light weight materials as TiAl based alloys need to be protected by different protective coatings with a reservoir of Al and Cr. Further this book presents interdiffusion modelling studies based on Darken concept. This book describes is an excellent reference for materials scientists and engineers that need more knowledge about high temperature resistance of TiAl based alloys.