Abstract: El Niño–Southern Oscillation (ENSO) influences global weather and climate through teleconnection patterns. In tropical regions, ENSO can induce precipitation and sea surface temperature anomalies over remote ocean basins by influencing tropical tropospheric temperatures; meanwhile, in extratropical regions, it can create climate impacts over regions such as North America and Asia by exciting quasi-stationary Rossby waves. Background mean-state fields are of vital importance to the tropical and extratropical teleconnections of ENSO. On the one hand, background mean-state atmospheric circulations can affect the position and intensity of ENSO teleconnection wave trains via barotropic and baroclinic energy conversion. On the other hand, sea surface temperature and convection fields of tropical background mean-state can affect the tropical teleconnection processes of ENSO by adjusting the moist static energy distribution. These studies suggest that an analysis of energetic processes can help understand the mechanisms by which background mean-state fields influence ENSO teleconnections. The present study reviews the progress of energetic analysis research regarding the effects of background mean-state fields on the tropical and extratropical teleconnections of ENSO in recent decades. Accordingly, potential changes in ENSO teleconnections are further reviewed in the context of global warming and some important scientific questions are listed, which warrant future investigation.