International audienceThis paper is based on an investigation of the Sraffa Archives and tries to characterise Piero Sraffa's approach to business cycles and economic policy. It includes two parts. The first part of the paper shows the importance of economic institutions and social conventions in Sraffa's contribution to economics and their relation with social conflicts. The second part of the paper shows how this importance permits to understand better business cycles and economic policy but also indirectly contributes to a re-interpretation of Sraffa's contribution to economics