High-entropy two-dimensional materials (HE2DMs) have emerged as a transformative class of electrocatalysts for efficient and sustainable electrochemical water splitting. By incorporating five or more principal elements in near-equimolar ratios within atomically thin 2D frameworks, HE2DMs uniquely combine the advantages of configurational entropy stabilization with the high surface area and tunable electronic properties of 2D materials. These materials demonstrate enhanced catalytic activity and stability in both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), outperforming many conventional and noble-metal-based catalysts. The high entropy effect introduces lattice distortions and abundant active sites, while the synergistic interactions among multicomponent elements optimize the adsorption energies of reaction intermediates. This chapter comprehensively explores the synthesis strategies, structural and electronic design principles, and mechanistic insights governing HE2DM performance in water splitting. We also highlight recent experimental and theoretical advancements, including density functional theory (DFT) and machine learning-guided material discovery. Despite current challenges related to scalability, phase control, and long-term durability, HE2DMs hold significant promise for large-scale, cost-effective green hydrogen production. This work provides a foundational understanding to guide future research in the rational design and development of HE2DMs as next-generation electrocatalysts for clean energy technologies.