Different theoretical models have been proposed aiming to describe the swelling behavior of microgels. Macroscopic gel models have been used for describing the swelling of microgels suspensions, where gel electroneutrality is assumed and the effect of the self-repulsion of the backbone charges on the chain conformation is neglected. Furthermore, these theories are restricted to microgels with relatively uniform charge distributions across the entire network. Scaling and phenomenological models have been proposed and contrasted against coarse-grained simulations for exploring the role of the screened electrostatic interactions between backbone charges upon swelling in nanogels. More sophisticated theories, such as density function theory and variational theory, have been developed and investigated, to consistently relate microscopic degrees of freedom with microgel swelling. Here the complex coupling between microgel screening, backbone self-repulsion and polymer conformation has been accounted for. Particularly, Denton and Tang have introduced a mean-field cell-model-based framework that links the continuous variations in the counterion density with conformational variation of the polymer and the influence in the microgel electrostatic charge density. The latter has proven to accurately describe swelling for weakly charged microgels with sizes of a few hundred nanometers. Deepening the understanding of smaller microgels becomes pertinent since this scale of sizes can accentuate features that unfold new potential applications. These new aspects at smaller length scales have been explored. It has been shown that nanogel swelling is governed by screened electrostatic interactions without a relevant contribution by the counterion osmotic pressure. The reduced screening due to entropic effects leads to strong self-repulsion of the backbone charges, which impacts chain elongation.