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We study the actual process of technical change in the case of NOx abatement from large stationary sources that have been regulated by very forceful policies in Sweden. Considerable progress has been made in lowering aggregate emissions and this paper seeks to disaggregate average industry improvements to study how much of it is due to innovations by first movers, and how much is achieved by adoption and diffusion of technology. We find both factors very important. Innovation has been rapid: the best firms have cut emissions on the order of 70%. In spite of this, reductions have actually been even more rapid for the majority of firms so that the median firms have caught up with best practice. We analyze various characteristics of the technological change observed.