Low-carbon energy systems is an academic concept and interdisciplinary research field focused on the design, analysis, and implementation of energy infrastructures and technologies engineered to significantly reduce greenhouse gas emissions, primarily carbon dioxide, throughout their lifecycle compared to traditional fossil fuel-dependent systems. This field investigates the technical integration, economic viability, environmental performance, and socio-political dynamics associated with transitioning towards energy mixes dominated by sources and technologies characterized by inherently low or zero operational carbon emissions, such as renewable energy, nuclear power (fission and fusion), and energy efficiency measures, often incorporating smart grid technologies and demand-side management. Its significance stems from its central role in addressing global climate change, enhancing energy security, and fostering sustainable energy transitions.