Most stocks can be traded on multiple exchanges. At a given time, the price for a stock will not necessarily be the same on all exchanges.
With Smart Routing, your orders are automatically sent to the exchange offering the best execution conditions at that moment.
To determine the exchange destination of an order, Interactive Brokers' smart routing takes into account several factors such as: the best bid or ask price, speed, probability of execution, size and type of your order, and execution costs.