Across the world, the supply for financial services rarely matches the demand, given multiple market frictions. This paper discusses the concept of the financial possibilities frontier as a constrained optimum to categorize different problems of shallow financial markets or unsustainable expansion. The paper offers three examples of how to use different data sources to apply the frontier concept to assess the state of financial systems. Households, enterprises, and governments demand financial services to reallocate consumption and investment across different time periods and different states of the world. The fact that the financial sector is one of the oldest service sectors in human history suggests that the demand for (i) payment, (ii) savings, (iii) credit, and (iv) risk management services are a fundamental characteristic of exchange-based economies. Micro-evidence in the form of financial diaries (Collins et al., 2009) has shown that even the poorest of the poor have demand for financial services, even though this demand is satisfied mostly by informal arrangements.