Most of us take for granted that those rectangular green slips of paper we keep in our wallets are inviolable: the physical embodiment of value. But alternative forms of money have a long history and appear to be growing in popularity. It's not merely barter or primitive means of exchange like seashells or beads. Beneath the financial radar, in hip U.S. towns or South African townships, in shops, markets and even banks, people throughout the world are exchanging goods and services via thousands of currency types that look nothing like official tender. Alternative means of trade often surface during tough economic times. When money gets dried up and there are still needs to be met in society, people come up with creative ways to meet those needs," says Peter North, a senior lecturer in geography at the University of Liverpool and the author of [a book] on the subject. He refers to the "scrips" issued in the U.S. and Europe during the Great Depression that kept money flowing and the massive barter exchanges involving millions of people that emerged amid runaway inflation in Argentina in 2000. "People were kept from starving [this way]," he says. Closer to home, "Ithaca Hours," with a livable hourly wage as the standard, were launched during the 1991 recession to sustain the economy in Ithaca, N.Y., and stem the loss of jobs. Hours, which are legal and taxable, circulate within the community, moving from local shop to local artisan and back, rather than leaking out into the larger monetary system. The logo on the Hour reads "In Ithaca We Trust." Alternative (or "complementary") currencies range from quaint to robust, simple to high tech.