We investigate whether the returns of some industry portfolios predict the returns of other industry portfolios. We find a strong lead-lag structure which is statistically and economically significant. These findings suggest that information diffuses only gradually across industries. Moreover, we show that this predictability can be exploited in a mean-variance optimization framework. The calculated out-of-sample portfolio returns are attractive under different return-risk measures, and they show positive risk-adjusted excess returns which are not explained by classical risk factors.