Why did Victorian Britain send so much capital abroad? We collect over 500,000 monthly British and foreign security returns between 1866 and 1907 and investigate the effect of international diversification on Victorian investors’ portfolios. This is the first study to use nineteenth-century data that is both broad enough and sampled at a high enough frequency to examine if foreign assets expanded the mean-variance efficient frontier of British investors and how valuable this expansion was in terms of utility. We find that foreign assets significantly expanded the mean-variance frontier and resulted in utility gains equivalent to large increases in wealth.