This lecture introduces the concept of green buildings within the broader context of modern architecture and global sustainability challenges. It traces the historical background of environmental awareness in the built environment, beginning with the 1973 global energy crisis, the growing recognition of carbon emissions and climate change, and the emergence of international sustainability frameworks. The lecture also discusses key milestones such as the Brundtland Report, BREEAM, LEED, and the Paris Agreement, highlighting how buildings contribute significantly to global carbon emissions. It further explains the principles of sustainable and green building design, emphasizing life-cycle thinking, energy efficiency, embodied and operational energy, and the role of architecture in reducing environmental impact.