The development of the MMA process is a rare case in which the first process developed in the 1930s dominates its world production even today. But now, several new methods have been realized mainly by Japanese companies. The various processes described above had to or will have to make jumps in catalysts performances in order to rise up to an industrial eco- nomically favorable level, though the reactions them- selves have been studied for a long period. It will be interesting to see which process will be the main stream of the MMA manufacturing from now on. Cat- alyst researchers all over the world are expected to develop new catalysts for such a process and then the commercialization will be verified