Nearly 2.5 billion people--half the world's adult population--lack one of the most basic amenities of modern life: a bank account. They are among the world's poorest, struggling to obtain the money they need to feed their families or start a business and create jobs. Their exclusion from the modern financial system represents a significant obstacle in the global effort to end extreme poverty and boost shared prosperity. That's why World Bank Group President Jim Yong Kim has called for universal access to finance by 2020--an urgent reminder that this challenge can be overcome in this generation. Governments play a critical role but they can't do it alone. It will take a concentrated effort by the private sector, which now accounts for less than...