Energy Internet is a new development form of energy system. It realizes the integration of energy flow, information flow and business flow. More and more business model and service model innovations are stimulated in Energy Internet. In this paper, we present a systemic study of Energy Internet from the business perspective. We first propose the evolution stages of energy systems. Since they were invented in the second industrial revolution period, energy systems have mainly experienced four stages, i.e., decentralized energy system, centralized energy system, distributed energy system and smart & connected energy system. Energy Internet is the innovative representation of energy systems in the fourth development stage. We also introduce some key concepts in Energy Internet, including prosumer, micro grid, Virtual Power Plant (VPP), smart grid and smart energy. Then the business values of Energy Internet are discussed from the energy big data analytics perspective. Finally, the business research agendas of Energy Internet are pointed out from five aspects, i.e., strategic issues, data issues, behavioral issues, security issues and regulatory issues. (C) 2016 Elsevier Ltd. All rights reserved.