For order-driven exchanges, the exchange will make public a list of unmatched trades which have been placed to that exchange, which is referred to as the order book. On the left hand side of the order book is the unmatched by orders. These are ranked by price with the highest price, the most that someone's willing to pay to buy some shares, ranked at the top of the list. The size of the order is irrelevant in terms of the ranking. And in the example on the screen, the most that someone is willing to pay to buy 5,000 shares in Company A's stock is $105. There is another order at 104, and a third order at 103. On the right hand side of the order book are the sell orders. These are also ranked by price, but in ascending order. The sell trade that is most likely to be matched is the one with the lowest price. The counts party that is willing to receive the least for delivering their shares. Again, size of order is irrelevant. The lowest price that someone is willing to receive here is $107 per share. There are two sell orders at 109. These would be ranked, but by the time of the order with the earlier order being ranked higher. Nothing would change in this order book until a new order was placed or one of the existing orders was canceled or deleted before it was matched. To demonstrate what would happen if a new order was placed, let's imagine a limit order to buy 5,000 shares at $109 was placed. This will be matched initially against the existing sale order for 2,500 shares at a price of 107 and would be executed at that price of 107. The remaining 2,500 shares of the buy order can now be matched against the next order down on the sale side at a price of 109. This sell order was for 3000 shares but now 2,500 of those have been matched, meaning that only 500 of those shares remains. Orders can be partially matched.