This chapter discussed optimal h-refinement preconditioning strategies, leveraging Calderón identities, for some of the most widespread IEs: the EFIE, CFIE, and PMCHWT. The treatment has been kept accessible by providing the main insights into the curing mechanisms and effectiveness of the schemes. Because the Calderón identities also provide a partial regularization of the low-frequency ill-conditioning and numerical issues affecting these equations, the coupling of the Calderón strategies with quasi-Helmholtz projectors - that make this partial stabilization complete - have also been presented. To ensure that the reader can make the most out of the techniques presented, we have consistently provided discretization strategies for the different schemes, with a particular focus on the PMCHWT for which several alternatives were introduced, along with numerical examples illustrating the effectiveness of the schemes.