This chapter shows how a marginal analysis of social welfare optimization reveals the incentive and sharing structure of socially optimal solutions. This analysis measures the extent to which stakeholders are incentivized to improve the efficiency with which they use resources, where the incentives consist of larger resource allotments in the socially optimal solution. It also indicates when a given fairness criterion incentivizes cooperation or competition among stakeholders. Finally, it shows how efficiency-improving investments are best allocated to stakeholders.