An order to purchase all shares available in the market for a particular stock at the current selling price. A buy the book order is most likely to be made by an institutional investor, and is generally to be executed at the current market price. Shares can be purchased from any party interested in selling. Taobiz explains Buy The Book "Book" refers to the record of positions kept by a broker or specialist before the advent of computers. It was a record of all shares owned, so buying the book meant that an investor was taking all the broker's shares off his hands. This type of trade can end up being a very large trade in high volume stocks and may increase the price other investors are willing to sell at.