Yup, there's usually a primary exchange, but a stock can be traded on many exchanges. Years ago people could make money via arbitrage between exchanges. Essenti

Yup, there's usually a primary exchange, but a stock can be traded on many exchanges. Years ago people could make money via arbitrage between exchanges. Essentially if stock ABC costed $50 at one exchange, but people were willing to buy ABC at $55 on another exchange, a quick trader could buy the stock at $50 on one exchange, and sell the equivalent on the other exchange for $55, making a "free" $5 without any change in their holdings. Now that we have computerized trading solutions the price difference between exchanges is essentially nil and cannot be taken advantage of unless you have ultrafast computers and access to fiber optic networks.