The built environment encompasses human-made structures, from bridges and pipelines to office towers and residential buildings. The built environment is so omnipresent that we do not perceive it as a distinct entity within the larger natural environment, the Earth’s biosphere. This chapter outlines the origins of buildings and the current primary drivers in the built environment, including sustainability, resilience, and smartness. The discussion will focus on building envelopes as environmental mediators between the indoor and external environments. Because building envelopes are essential in providing an appropriate indoor environment, they also directly influence energy use for heating, cooling, and lighting, thus affecting greenhouse gas emissions. Speaking globally, buildings consume vast amounts of energy, have a significant environmental impact and are, at least in the urbanised part of the world, our primary habitat. Therefore, it is crucial to design them in a way that enables a more sustainable future for generations to come. However, buildings themselves are not the problem, but only a symptom of our society. To appreciate why and how we build, we need to understand the broader picture.