A system and method for providing back-end functionality for order processing in electronic order book trading. A sell/buy order is received comprising a lower/upper limit and a conditional lower/upper limit defining a conditional selling/buying price range for executing the sell/buy order under certain selling/buying conditions. It is determined whether the selling/buying conditions are fulfilled, including determining whether the sum of the first and second part of the buy/sell order is superior or equal to a threshold volume. The sell/buy order and the buy/sell order are executed against each other if at least the selling/buying conditions are fulfilled. Embodiments allow rapidly executing large trading interests with minimized market impact and opportunity costs.