????How to make sure the cotton in your shirt wasn't picked, say, by child laborers.

????By Marc Gunther

????Where was the cotton in your shirt grown? Who mined the gold in your wedding ring? What forest produced the paper in the magazine you are reading?

????You almost surely don't know, but a growing number of brands and retailers want to dig deep into their supply chains to better understand the roots (sometimes literally) of the products they sell. Their goal: to avoid risks and enhance their reputation as "green" business leaders, says Tim Wilson, the 41-year-old CEO of Historic Futures, a little British company that is riding a big idea in sustainability, known as traceability.

????Using Internet-based systems and RFID tags, Historic Futures tracks such commodities as cotton and gold through the long and previously opaque supply chains of Wal-Mart (WMT, Fortune 500), Gap (GPS, Fortune 500) and Patagonia, among others. "If you don't know where your stuff is coming from," Wilson asks, "how can you have a sustainability program?"

????So, for example, Wal-Mart's "Love, Earth" brand of gold and silver jewelry invites consumers to visit a website to find the source of their precious metals - and to be assured that it's not a dirty mine in a poor country.

????Patagonia's "Footprint Chronicles" website tracks the journey of a T-shirt through the global economy, revealing its carbon footprint, water usage and miles traveled. The British retailer Tesco (TESO), which has pledged not to sell anything made with cotton picked by child laborers in Uzbekhistan, now traces its dry goods through several tiers of suppliers to make sure it can keep its word.

????Wilson, who previously wrote software for farmers, came up with the idea for Historic Futures after mad cow disease devastated the British beef industry. The outbreak began with as few as 100 sick cows, but no one knew how to find them.

????His company's tagline - "The Future is History" - is not an apocalyptic prediction but an expression of the idea that brands and consumers eventually will want to understand the history of everything they buy.