We investigate the geographic concentration and agglomeration of production activity in the UK at the four-digit industry level using a variety of measures. We relate these to comparable patterns in the US and France and find several similarities. We find that conditioning on industrial concentration, the most geographically concentrated industries appear to be relatively low-tech. We find evidence that plant survival rates are higher and both entry and exit rates lower in more agglomerated industries, but that in some of the most agglomerated industries entry acts to re-enforce agglomeration.