  This is the companion article to the Bourbaki talk of the same name given in
March 2009. The main theme of the talk and the article is to explain the
interplay between homotopy theory and algebraic geometry through the
Hopkins-Miller-Lurie theorem on topological modular forms, from which we learn
that the Deligne-Mumford moduli stack for elliptic curves is canonically
realized as an object in derived algebraic geometry.
