This paper addresses reasons for innovation. Innovation requires resources to transform new ideas into products/services to be sold in the market and diffused in society. Yet in the earlier stage of innovation process uncertainty always prevails both technologically and economically. There is no objective consensus that the new idea will succeed in the end. It is thus necessary for those people who want to realize the innovation to show others both inside and outside the firm legitimate reasons for mobilizing their precious resources, including people, materials, facilities, and money, throughout the process toward commercialization. How do firms legitimize the resource mobilization for innovation? Drawing on 18 case studies on Okochi Memorial Prize winners, which our joint research project has carried out over last five years, and building upon the existing literature on internal corporate venturing, new ventures, and other related issues, this paper examines the innovation process of established Japanese firms from idea generation to commercialization with a primary focus on the process by which resource mobilization was legitimized.