The European Common Fisheries Policy Reform includes new discard regulation that is likely to have the greatest impact on fisheries and fleets of any recent regulation. However, there is a distinct lack of data or empirical knowledge available to inform the effects on fleets. This has the potential to result in a step change in fishing behaviour. There is much written on the economics of discards, for example the knowledge of what is rational behaviour regarding discarding Vs incentives driven by policy not to discard. In this paper, we consider what fisheries economics theory tells us as well as exploring gaps in our knowledge regarding a discard ban. We use an empirical example of the North Sea demersal fisheries to consider implications further.