abstract: We consider certain variational problems involving 1-dimensional connected sets (e.g. the Steiner-Gilbert and the Steiner tree problem) and provide variational approximations via Gamma convergence by means of functionals of phase transitionGinzburg-Landau type. We then consider a suitable convex relaxation procedure and present the corresponding numerical implementations both in 2 and 3 dimensions. This is joint work with Giandomenico Orlandi (Verona) and Edouard Oudet (Grenoble).