A hotel that's part of this collection has been officially certified to a sustainability standard by an independent organisation. The organisation's standards are either recognised by the Global Sustainable Tourism Council (GSTC) or the organisation itself has been accredited by the GSTC. The standards cover several things these hotels do, such as management, impact on local communities, supporting local heritage and actions to reduce environmental effects. To get more clued up, head to the GSTC website.