World leaders gathering this week for the G-20 summit, the 64th United Nations General Assembly and the Clinton Global Initiative conference are faced with major economic challenges. As they grapple with these issues, there is one fundamental principle that must not be forgotten: We cannot build a viable global economy on an unstable base.In real terms, the global economy is asymmetric because roughly half of the world is excluded from fully taking part in it. Half the worlds population doesnt have access to the rudimentary financial services that most of us take for granted things like a bank account or basic financial tools such as life insurance or a reasonable short-term loan. Some 3 billion people are cut off from the formal financial sector, effectively separated from the greater economic ecosystem.This phenomenon is more prevalent in areas of the developing world, but it is by no means restricted to those places. In the United States, 28 million people are unbanked. While our own situation is troubling enough, it pales in comparison to India, where 410 million people are unbanked, and sub-Saharan Africa, where a staggering 80 percent of the population is excluded from accessing basic financial services.One of the simplest yet least appreciated ways of addressing the global economic crisis is to get the worlds money out from under mattresses and into banks, where it wont sit idly, cant be stolen, go up in smoke or be used to fuel the black market. Instead, that money can earn interest, buy goods, circulate freely, create value, and lift lots and lots of boats. In recent years, many organizations, such as the U.N., CGI and the World Bank have stepped up efforts to link the unbanked to financial services and systems that can help them make economic progress. We believe that Visa and others need to step up to support their efforts.Our company takes financial inclusion seriously. Its vital that people have access to financial services in order for them to prosper. This is our version of what Bill Gates termed creative capitalism, which will drive market-based social change. Before you dismiss this as impossible, consider that digital technology, particularly with mobile phones, can accelerate financial inclusion by enabling electronic money transfers and remittances, microlending and secure ways to save in even the most remote parts of the world.Some dismiss the 40 percent of the world who live on less than $2 a day as unsophisticated and uninterested in financial services, but the recently released book, Portfolios of the Poor, paints a much different picture. The worlds poor are some of the most innovative and vigilant money managers around. They have to be. In the face of scant resources, limited services and uneven consumption, the poor rely on a complex and ingenious web of family, community, sophisticated savings clubs and microfinancing, when available.