Advanced nuclear reactors is a research field and engineering discipline focused on the design, development, and evaluation of next-generation nuclear fission reactor technologies that significantly advance upon existing designs. This concept investigates novel reactor architectures, fuel cycles, coolants, and safety systems aiming for enhanced safety (often passive), increased thermal efficiency, optimized fuel utilization, reduced waste generation, improved economic competitiveness, and inherent proliferation resistance, representing a critical area in the pursuit of sustainable and secure low-carbon energy solutions.