The traditional way of economic and social development，characterized by centralized utilization of fossil fuel energy，is gradually changing.On the other hand，the third industrial revolution is now rising.As the core technology of the third industrial revolution，the Energy Internet aims at facilitating large-scale utilization and sharing of renewable energy by integrating renewable energy and internet technologies.It will enhance the merging of electricity，transportation and natural gas networks，change the way of energy utilization，and finally achieve the goal of promoting sustainable economic and social development.Given this background，an overview of the Energy Internet is first provided，and a basic research framework developed.A definition of the Energy Internet is then suggested，followed by its basic architecture and main components.Several main research challenges to the Energy Internet，such as the wide-area coordination and control of distributed devices，the integration of the power system with the transportation system and natural gas network，as well as the cyber physical modeling and security，are next discussed in more details.