Materials with atomically dispersed metal sites (ADMSs) have been recently intensively studied as electrocatalysts for various energy conversion reactions. The well-defined and tunable compositions and structures of the ADMSs offer great opportunities for rational design and fabrication of ADMS-based electrocatalysts with unique electrochemical properties superior to conventional electrocatalysts. Recent progress in this field has demonstrated the potentials and superiority of the practical use of ADMS-based electrocatalysts for energy conversion. However, this field is still in its infancy with a large room for improvement. This review provides general strategies to improve the electrocatalytic performances of ADMS-based electrocatalysts such as precisely controlling the compositions and structures of ADMSs and finely tuning the interactions between ADMSs and supports. An overview of recent developments of ADMS-based electrocatalysts for specific energy conversion reactions including oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), oxygen evolution reaction (OER), carbon dioxide reduction reaction (CO2RR), and nitrogen reduction reaction (NRR) is presented, while the main challenges and future directions in this field are also discussed.