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Global symmetry plays a crucial role in the study of QFT. Recently, various generalizations of the concept of global symmetry has been proposed. In the talks I would like to discuss the notion called “categorical symmetry”, or various other names, particularly in 1+1 dimensions. Such a “symmetry” lacks its inverse, and described by the mathematical concept of a fusion category, instead of a group. Physically it refers to the collection of all the topological line defects exists in the 2d QFT. A “categorical symmetry” is preserved along an RG flow, as an ordinary symmetry and its ’t Hooft anomaly does, which is crucial in its applications. It sometimes admits the notion of “gauging”, too.