Geometrical theory, electronic theory, semiconductor theory, which are classic theories of catalysis phenomena are introduced. Theoretical considerations of catalysis phenomena will be given applying molecular orbital theory now in progress. The correlation of catalytic properties such as activity and selectivity with the performance of catalyst is discussed. Instrumental methods to analyze the reaction intermediate and structure of catalyst are intermediate and structure of catalyst are introduced. This course also covers the theoretical interpretation of both the homogeneous and heterogeneous catalyst.