This paper wants to demonstrate the contribution of Giuseppe Toniolo to the formalization and implementation of the principle of subsidiarity. After a quick overview on the historical, political, economic and social background between the unification of Italy and the First World War, this work examines the thought of Giuseppe Toniolo about the open issues of his time, under the light of the principle of subsidiarity. At the end, the legacy and relevance of the cultural and scientific contribution of the Pisan economist are briefly outlined.