<p>Increasing power densities in microprocessors and artificial intelligence hardware are pushing the thermal limits of electronic systems, and thermal interface materials—thin layers that conduct heat between dissimilar surfaces—are central to addressing this challenge. Classical models suggest that efficient heat transfer is possible with such materials, but real-world performance is always limited by nanoscale roughness, imperfect contacts and degradation under thermal cycling. Here we explore the development of thermal interface materials. We examine the physical origin of interfacial thermal resistance and consider its impact on device scaling, efficiency and reliability. We then discuss material and design strategies that can balance thermal conductivity with mechanical compliance, bond line thickness and electrical insulation. Finally, we highlight the need to treat thermal interface materials, not as passive fillings, but as integral system components that are co-designed alongside device architectures, and propose an integrated engineering framework for the future development of thermal interface materials.</p>