El Ni?o-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. In extratropical regions, ENSO can pose climate impacts over regions such as North America and Asia through the excitation of quasi-stationary Rossby waves. The background mean-state fields are of vital importance to ENSO"s tropical and extratropical teleconnections. On one hand, the background mean-state atmospheric circulations can influence the position and intensity of ENSO teleconnection wave trains through barotropic and baroclinic energy conversion. On the other hand, the tropical background mean-state sea surface temperature and convection fields can influence ENSO"s tropical teleconnection processes through the adjustment of moist static energy distribution. These studies suggest that analyzing energetic processes can help to understand the mechanisms through which the background mean-state fields influence ENSO teleconnections. The present study reviews the progress in energetic analysis researches on the impacts of the background mean-state fields on ENSO"s tropical and extratropical teleconnections in recent decades. Based on it, this study will further review the potential changes of ENSO teleconnections under global warming, and propose some important scientific questions that need to be studied in the future.