Electroencephalography (EEG) is a technique for non-invasively measuring neuronal activity in the human brain using electrodes placed on the scalp. However, the low spatial resolution of standard EEG limits accurate localization of brain activity sources. High-Resolution Electrical Source Imaging (ESI) techniques integrate high-density EEG with source localization algorithms, enabling a more spatially precise reconstruction of volumetric brain currents, thus establishing ESI as a valuable tool for brain imaging and diagnostics. This thesis provides an in-depth validation of different ESI techniques, focusing on testing and comparing their accuracy and resolution. It tackles both theoretical and practical challenges through a computational and experimental assessment.