There are many well-documented examples of how our ancestors successfully used their surroundings to sculpt sustainable built environments. Attention to natural energy flows and to the properties of local materials was rewarded with comfortable shelters and small ecological footprints. However, over a time span of a few decades communities around the world have lost, or 'misplaced' much of their cultural knowledge. This has led to the adoption of many 'standard' practices that are not necessarily suited to the local context. While case studies demonstrate that architecture, planning, design and materials are all undergoing 'dramatic sustainability breakthroughs', why is our built environment generally becoming less comfortable and more resource hungry? This chapter explores the barriers and opportunities to greening the built environment. Mentoring and assistance for this chapter was gratefully received from Professor Alan Pears and Dr Janis Birkeland.