To improve quality and production yield of various electronic devices (such as semiconductors, displays, and storage media), it is necessary to ensure a precisely controlled environment in which cleanliness, temperature and so on are controlled in accordance with the needs of the fabrication process. In recent years, the trend for advanced environmental control of the minimum required clean-room space only has become more pronounced. Accordingly, in line with this trend, Hitachi Group has been developing clean-room technologies from the viewpoints of both large-space (i.e. "ballroom-type") and localized clean-room environments. As "total clean technologies" to satisfy various requirements, several technologies are described in this paper. That is to say, to handle ballroom-type environments, a "return-ductless" clean room (which has relaxed cleanliness and good floor-space efficiency) is provided. Moreover, to handle localized-type precision environments, technologies such as systems for not only efficiently eliminating particulate contamination as a matter of course but also molecular contamination like various chemicals and water molecules (namely, a "chemical-free environmental system" and a "low-dew-point environmental system") and high-precision temperature-control systems are being provided.