Massachusetts is the most energy-­efficient state for the second year in a row, according to rankings by the American Council for an Energy­Efficient Economy.

This is the sixth year the council, a nonprofit advocacy group in Washington, has rated states according to criteria such as utility programs, state initiatives, policies, and building codes aimed at improving energy efficiency. The council said the state’s Green Communities Act — one of several pieces of environmental legislation passed in 2008 — contributed to Massachusetts’ keeping the number one spot.