Contrary to bookmaker and totalisation systems, betting exchanges offer the opportunity to lay, which is to bet that a selection will not occur. This is the position bookmakers have traditionally taken when offering a bet to somebody to back that the outcome will win.

As every bet transacted requires a backer and a layer, and the betting exchange is not a party to the bets transacted on it, any betting exchange requires both backers and layers. Of course, the distinction is moot: A layer is always simply backing that the event will not occur. Laying the home team is the same as backing the visiting team to win or draw. Laying one horse in a race is just the same as backing all of the other horses to win.