History of industries is one of the most intensively studied topics in the business history. However, there are only few works that deal with the most basic question; what is an industry? This paper examines this question by linking it with another question; “What kind of methodology and key categories are essential for studies on history of industries?” This paper starts with key elements, which forms the boundary of industries. Roles of 1)product, 2)technology and knowledge, 3)function in the economy and 4)market (geographical and social), shall be discussed. In the second section, this paper uses three cases to elucidate the importance of a “industry history view”. The first is a debate in Japan on uses and risks of (over-) application of the “architecture” concept in automobile and some process industries. The second is an implication of comparative studies on paper and steel industry, focusing on the industry-specific consumption pattern and nature of the product. The third case is a transformation of the screw industry for the automobile parts industry (industrial fastener supplier) and possibility to introduce a new concept, “versatile supporting industry”. All three cases suggest systematic attention to the specificity of each industry and conscious application of basic categories are highly important.