Carbon-based nanoparticles have recently generated a great attention, as they could create polymer nanocomposites with enhanced transport properties, overcoming some limitations of electrically-conductive polymers for high demanding sectors. Particular importance has been given to the protection of electronic components from electromagnetic radiation emitted by other devices. This review considers the recent advances in carbon-based polymer nanocomposites for electromagnetic interference (EMI) shielding. After a revision of the types of carbon-based nanoparticles and respective polymer nanocomposites and preparation methods, the review considers the theoretical models for predicting the EMI shielding, divided in those based on electrical conductivity, models based on the EMI shielding efficiency, on the so-called parallel resistor-capacitor model and those based on multiscale hybrids. Recent advances in the EMI shielding of carbon-based polymer nanocomposites are presented and related to structure and processing, focusing on the effects of nanoparticle’s aspect ratio and possible functionalization, dispersion and alignment during processing, as well as the use of nanohybrids and 3D reinforcements. Examples of these effects are presented for nanocomposites with carbon nanotubes/nanofibres and graphene-based materials. A final section is dedicated to cellular nanocomposites, focusing on how the resulting morphology and cellular structures may generate lightweight multifunctional nanocomposites with enhanced absorption-based EMI shielding properties