We characterize optimal firm-specific emission tax rates, and optimal firm-specific emission standards, and provide intuitive explanation on differential treatments. We show that there is a unified framework for deriving firm-specific policy measures. When firms are identical, the optimal policy may call for unequal treatments of equals. When firms are not identical, we characterize the optimal degree of dispersion of tax rates. The unequal treatments of unequals is explained in terms of the motive of the government to affect industry concentration. Our new approach is geometric in nature and enables us to give optimality conditions in global terms.