Roughly one-fifth of the world's population currently lives -- or tries to -- on less than $1 a day. That is a crude measure, but it translates into a daily grind of hunger, misery and disease that no human being should have to endure.

Last September, at the U.N. Millennium Summit, world leaders resolved to "spare no effort" to free their fellow human beings "from the abject and dehumanizing conditions of extreme poverty." Specifically, they pledged to halve the proportion of the world's people living in those conditions by 2015.

Probably no single change would make a greater contribution to fulfilling that pledge than fully opening the markets of prosperous countries to the goods produced by poor ones.