Abstract. Let L be the Laplacian on R^n . The investigation of necessary and sufficient conditions for an operator of the form F (L) to be bounded on L^p in terms of smoothness properties of the spectral multiplier F is a classical and very active research area of harmonic analysis, with long-standing open problems (e.g., the Bochner–Riesz conjecture) and connections with the regularity theory of PDEs. In settings other than the Euclidean, particularly in the presence of a sub- Riemannian geometric structure, the natural substitute L for the Laplacian need not be an elliptic operator, and it may be just sub-elliptic. In this context, even the simplest questions related to the L^p -boundedness of operators of the form F (L) are far from being completely understood. I will survey recent results dealing with the case of sub-Laplacians on 2-step Carnot groups, complex and quaternionic spheres, and Grushin operators.