Can prices ever be too low? US and EU lawyers and economists have long debated when the antitrust agencies and courts should step in to prevent prices that are “too low.” There is a consensus that, in some circumstances, low prices can be harmful to competition. Nonetheless, economists and lawyers have not been unanimous on the exact conditions that should be used to define when pricing is predatory and when the agencies and courts should intervene. This paper sets out the basic principles and ideas that any policy on predatory pricing should follow, and puts forward a series of specific tests. In addition, the authors examine if and how these tests could be applied in China.