The energy "Trilemma" seeks to develop an electricity market which simultaneously ensures environmental quality, security of supply, and economic sustainability. The objective of this paper is to present the "Trilemma" energy as the latest trend in the design of energy policy. For this, a theoretical framework is presented in sections 2 and 3, in section 4 and 5 the importance of security of supply and economic sustainability are discussed, respectively. In section 6 the energy "trilemma" is presented, in section 7 a brief state of the art is showed. Finally in section 8, it is approached three different electricity markets. It is concluded that the regulator has passed in recent years from encouraging a liberalized market scheme, to promote a scheme based on intervention through policies that affect the market competitiveness but allow achieving its environmental goals.