Houses of worship serve as the spiritual centre for communities where they can practice religious rituals. Some estimates indicate that there are around 37 million churches, 4 million mosques, 20 thousand synagogues and hundreds of millions of temples in existence today. These places can become models of sustainability, engaging in eco-friendly practices of worship, sustainably designed buildings, and teaching an environmentally-friendly lifestyle within communities. This publication has been developed to showcase some successful examples from religions around the world on their greening efforts of their houses of worship and provide some useful references and tips to build or transform a house of worship to be green and contribute to achieving sustainability.