In the seminar I will present some joint work with T. Rivière where we study the Dirichlet energy of moving frames on 2-dimensional tori immersed in the euclidean $3\leq m$-dimensional space.  This functional, called Frame energy, is naturally linked to the Willmore energy of the immersion and on the conformal structure of the abstract underlying surface. I will discuss a ''Willmore Conjecture'' type lower bounds for such energy,  then I will introduce basic tools for doing the calculus of variations and finally I will give applications to regular homotopy classes of immersed tori in R^3.