Book excerpt: Handbook of Microfinance addresses the gap between clients who are benefiting from access to financial services via MFIs, and the potential market, which remains underserved or untapped. This gap can be attributed to a "mismatch" between what consumers, or potential clients, demand and what MFIs offer in terms of financial products. The scope of the book is wide. It includes successes and failures, main challenges and debates, methodologies for impact evaluation via random trials, leading trends in Asia versus Latin America, main efforts in Africa, the importance of value chains in Central America, ethical and gender issues, savings, microinsurance, governance, commercialization trends and the potential advantages and disadvantages of it. Lastly it features main lessons from informal finance and 19th-century credit cooperatives addressing the above-mentioned mismatch.