Abstract: Most legal academics and policy makers believe that notions of fairness should be accorded positive weight in evaluating legal policies. We explain, however, that ascribing importance to any notion of fairness (other than one concerned solely with the distribution of income) will sometimes lead to a conflict with the Pareto principle. That is, to endorse a notion of fairness is to endorse the view that it can be desirable to adopt a legal rule that will reduce the well-being of every person in society.