This paper examines market concentration and stock returns on the Australian Securities Exchange. We find that dominant companies operating in concentrated industries in Australia are able to generate significant risk-adjusted excess stock returns. Our results for Australian data are opposite to that found by Hou and Robinson (2006) for United States market data. Hou and Robinson reason that United States firms which operate in concentrated industries are insulated from competitive pressures, have lower levels of innovation (Arrow, 1962) and therefore experience lower profitability and stock returns. By contrast, the Australian data show a significant and positive relationship between concentration and innovation expenditure. Therefore, the excess stock returns of dominant companies in Australia are consistent with previous research linking innovation expenditure with excess stock returns. We hypothesize that the apparent contradiction of our results compared with Hou and Robinson (2006) for the United States market is resolved by an examination of the differences in size and competition in United States and Australian industries and the consequent differential ability of dominant companies in the two countries to generate monopoly rents and invest in 'Schumpeterian' (Schumpeter, 1942) innovation.