Polyamide 6 / layered silicate nanocomposite was manufactured as engineering plastics on a commercial basis in 1990. This was a starting point at the engineering level for our interest in polymer nanocomposites. This success initiated R&D efforts to investigate the possibility of combination of various polymers with various nano inorganic fillers. This field is considered to be a descendant of the past consecutive generation of science of colloid, science for interface-activated agents and polymer emulsion, and science and technology of polymer alloys, which could date back to 1910 to 1930, 1950 to 1970, and 1960 to 1980, respectively. Polymer molecular composites and polymer nanocomposites have been a target for R&D since 1970's. Much effort has been made to develop and apply polymer nanocomposites in transportation, electrical and electronics, food package, and building industries since 1990.