The major changes that have occurred in the steel industry are described along three periods: the thirty years boom-period after World War II; the zero growth period (1973-1983); the last period, from 1983 to nowadays. Under the heavy influence of the overall trends of world economy, these periods can be distinguished, for the steel industry, by the different levels of priority for productivity, for specific flat carbon steel product developments or for environmental protection. The intricate relations that prevail between the development of new processes, innovative product metallurgies and the requirements expressed by steel customers are highlighted.