When a company decides to cross-list, the stock is "technically" fungible between exchanges. Royal Dutch Shell, IBM, and Siemens are all examples where the same issue is traded in multiple markets. However, in Frankfurt and Paris, they are traded in EUR, London in GBP, and on NYSE in USD. Prices are subject to local market conditions, as well as FX fluctuations and are not kept in perfect parity between markets. They tend to be more liquid than ADRs, GDRs and those types of conventions. While 'technically' fungible, these separate primary listings (they would all be considered 'primary' listings) are subject to re-registration which creates significant settlement risk if an investor wants to buy on one exchange and sell in another (especially where the currencies differ).