This chapter explores the role of HTI in sustainable energy, through the lens of the Swedish Energy Agency’s ‘Design for Energy Efficient Everyday Life’ programme. This case study demonstrates the practical application of HTI principles in creating energy-efficient solutions, emphasising user-centric design and technological innovation. Through an analysis of various projects within this programme, the chapter delves into the complex interplay between human behaviour, technological advancements, and sustainability, namely on the perspective of energy efficiency. It assesses the impact of these projects on promoting sustainability, critically examining their methodologies and outcomes in energy conservation and environmental stewardship. The chapter concludes with a discussion about the role of sustainability in shaping HTI based on the findings and analysis from the programme’s outcomes.