In the 1980s, Witten introduced the Witten genus that assigns a modular form to each closed manifold with a string structure. Ando, Hopkins and Rezk showed that this refines to an E_infty-map MString -> TMF to the spectrum of topological modular forms. But their proof is very intricate. I will present a new approach to the string orientation via equivariant TMF, giving also an introduction to this theory.