abstract: We will present several results and techniques to study the regularity of optimal shapes. The outline of the lectures will be as follows: A) Classical results for the isoperimetric problems and on the regularity of quasi-minimizers (from the theory of minimal surfaces). B) A model problem: optimal shapes for the Dirichlet energy with prescribed volume. C) Adding surface tension. D) More examples. Optimal eigenvalues of the Laplacian, convexity constraints, polygons as optimal shapes.