Mainland China's two stock exchanges, in Shanghai and Shenzhen, both have A- and B-share markets. The key distinction is that A-shares are denominated in renminbi and B-shares in foreign currency (US dollars in Shanghai and Hong Kong dollars in Shenzhen). For a long time, the other main difference between the two, from a regulatory standpoint, was that the A-share market was closed to foreign investors while the B-share market was open only to foreigners. However in 2001, the Chinese authorities tried to boost the B-share market by opening it to individual Chinese investors. And in 2003, a scheme was introduced whereby select foreign institutions were allowed to buy A-shares. Some companies have their stocks listed on both boards, but their B-shares trade at a large discount to their A-shares, which tend to see much larger trading volumes.