Preface.- Biography.- Prizes and academic awards.- Teaching and academic commitment.- The activities out of Pisa.- Civil, religious and political commitment.- The scientific work of Ennio De Giorgi.- From the juvenile papers to Plateau’s problem and the solution of Hilbert’s19th problem.- Partial differential equations and the foundations of G-convergence.- Asymptotic problems in the Calculus of Variations.- The most recent developments in the Calculus of Variations.- The work on Foundations of Mathematics.- De Giorgi’s contribution to the regularity theory for elliptic partial differential equations, by Luis Caffarelli.- Remarks on some of the analytical work of Ennio De Giorgi, by Louis Nirenberg.- Complete list of De Giorgi’s scientific publications.- Selected papers.