The paper analyses the import and appropriation of Rawls's theory of justice into the emerging field of optimal taxation theory in the 1970s. It focuses first on the pioneer contributions of Atkinson and Phelps to integrate Rawls's maximin into optimal taxation models, and then on their numerous followers during this decade. It shows that the maximin criterion was quickly accepted and appropriated in optimal taxation theory using "Rawlsian" Social Welfare Functions, which are founded on a welfarist interpretation of the maximin, unfaithful to Rawls. I try to explain why public economists made this choice, insisting on issues of simplicity, tractability, and comparisons with other ethical criteria.