<p>Direct seawater electrolysis can use seawater and offshore renewable energy to produce hydrogen. However, the complexity of the composition and dynamics of seawater has hindered the transition from laboratory-scale breakthroughs to industrial scale. In this Perspective, we examine static and dynamic aspects of seawater and discuss four key strategies for scaling direct seawater electrolysis: electrocatalyst engineering, asymmetric electrolysis, aperture screening and phase-transition migration. To achieve long-term stable operation at industrial current densities (400 mA cm^–2 for 10,000 h) and large-scale hydrogen production capacity (386 l h^–1 for 3,200 h), challenges such as catalyst scale-up and performance maintenance, substance selection and the cost of asymmetric electrolysis, ion penetration and concentration polarization of osmotic membranes, and the driving force of phase-transition migration and membrane fouling need to be addressed at the technical and system levels. Technologies should integrate ion blocking with optimization of catalysts and membrane materials to achieve efficient and stable seawater electrolysis. In addition, to bridge the laboratory-to-industry gap of direct seawater electrolysis, it is necessary to customize an assessment framework that covers system design, sensitive conditions analysis and real-world validation based on the real ocean conditions.</p>