Silver is a tradead commodity that is usually considered side-by-side with gold as one of the two traded precious metals asset class that previously underpinned the value of the U.S. currency. Silver futures and spot contracts are traded OTC and on commodity exchanges like the CME Group and [NYSE LIFFE U.S.] while some investor buy shares in mining companies for exposure.
CME Group's silver futures contracts include a full-sized contract, which is 5,000 troy ounces, as well E-mini silver futures, which were launched in April 2009. E-mini silver futures are sized at 1,000 troy ounces. 
NYSE LIFFE U.S., which launched in 2008, purchased the former Chicago Board of Trade's (CBOT) silver and gold futures complex. Included in the deal were mini-silver and full-sized silver contracts which were, and still are, traded on the LIFFE Connect electronic trading platform. (LIFFE Connect was licensed by the CBOT, but that deal ended when the exchange was purchased by CME Group.) NYSE LIFFE U.S.'s full-sized silver futures is sized at 5,000 troy ounces per contract, mini-silver futures is sized at 1,000 ounces.