There is a sense of fairness that is distinctive of markets. This is fairness among economic competitors, competitive fairness. We regularly make judgments of competitive fairness about market participants, public policies and institutions. However, it is not clear to what these judgments refer, or what moral significance they have. This paper offers a rational reconstruction of competitive fairness in terms of non-domination. It first identifies competitive fairness as a distinctive claim, advanced within markets in turn characterised as antagonistic, instrumental and procedural. It distinguishes competitive fairness from a number of familiar ideals with which it might be confused: legitimate expectation, equality of opportunity, sporting fairness and economic efficiency. While many exponents likely assume competitive fairness can be explained in terms of one of these ideals, in each case there are significant objections to doing so. Instead, the paper argues that the most promising justification of competitive fairness is under the republican ideal of non-domination, which can reconstruct many of the intuitive judgments of competitive fairness that we make in particular cases. However, it concludes, this explanation makes it difficult for exponents to continue to emphasise competitive fairness, given diverse other risks of domination, and to other values, in markets.