Pierre Guillaume Frédéric Le Play was a French engineer, sociologist and economist.
For nearly a quarter of a century Le Play travelled around Europe, collecting a vast amount of information bearing on the social and economic condition of the working classes. In 1855, he published Les Ouvriers Européens, a series of 36 monographs on the budgets of typical families selected from a wide range of industries. This work was crowned with the Montyon prize conferred by the Académie des Sciences. In 1856, Le Play founded the Société internationale des études pratiques d'économie sociale, which has devoted its energies principally to forwarding social studies on the lines laid down by its founder. The journal of the society, La Réforme Sociale, founded in 1881, is published fortnightly.