Here's some more background info from CNN:
Mexico City becomes the second large metropolitan area in the Western Hemisphere to outlaw the bags. San Francisco in March 2007 enacted an ordinance that gave supermarkets six months and large chain pharmacies about a year to phase out the bags. Los Angeles is set to impose a ban if the state of California does not enact a statewide 25-cent fee per bag by July.
About 90 percent of the bags used in the United States are not recycled.
Bans and other restrictions on plastic bags are in place in several countries.
China has adopted a strict limit, reducing litter and eliminating the use of 40 billion bags, the World Watch Institute said, citing government estimates. Although compliance has been spotty, violation of the law carries a possible fine of 10,000 yuan ($1,463), World Watch said.
In Tanzania, selling the bags carries a maximum six-month jail sentence and a fine of 1.5 million shilling ($1,137).
Mumbai, India, outlawed the bags in 2000 and cities in Australia, Italy, South Africa and Taiwan have imposed bans or surcharges. Ireland reported cutting use of the bags by 90 percent after imposing a fee on each one.