Back to 2011 not so much bitcoin exchanges was exist. The most popular and biggest was MtGox who out of business due several hacking attacks and owner mismanagement. That was happened with several small exchanges all around the world. All those exchages operated without any regulation and license, because no rules was exist.
Today's we have several exchanges and markets: OKCoin, BTC China, Bitstamp, itBit, Bitfinex, Coinbase, Kraken, LocalBitcoins and etc... Almost all exchanges now has some sort of license for financial operations, because money operations with crypto-currencies now under government regulation in several countries. The biggest (by trading volume) exchanges now operated by Chinese owners.
Recommended bitcoin exchanges:
- LakeBTC.com - online wallet, exchange, trading
- LocalBitcoins - person-to-person bitcoin trading service