Alkaline water electrolysis is a key technology for producing green hydrogen, which is essential for a sustainable energy future. This review discusses the fundamentals and industrial developments of alkaline water electrolysis (AWE), focusing on the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The OER is more challenging than the HER, both thermodynamically and kinetically, and requires durable, abundant electrocatalysts. The performance of AWE depends on the catalyst's surface, interaction with water and reaction intermediates, and the formation of molecular hydrogen and oxygen. The review highlights recent advances in electrocatalysts, including the role of phase segregation, defect structures, and the e_g orbital filling in cobalt-based catalysts. It also discusses the development of new active surface species and the activation of cobalt- and nickel-based catalysts through iron uptake from the alkaline electrolyte. Challenges in large-scale production and utilization of green hydrogen are addressed, including the need for efficient, stable, and cost-effective electrocatalysts. The review emphasizes the importance of understanding the reaction mechanisms and physicochemical properties of catalysts to improve the efficiency and sustainability of AWE. The potential of new compositions and materials for enhancing energy efficiency and advancing the field of green hydrogen production is also discussed. Overall, the review underscores the critical role of AWE in the transition to a sustainable energy system and the need for continued research and development in this area.Alkaline water electrolysis is a key technology for producing green hydrogen, which is essential for a sustainable energy future. This review discusses the fundamentals and industrial developments of alkaline water electrolysis (AWE), focusing on the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The OER is more challenging than the HER, both thermodynamically and kinetically, and requires durable, abundant electrocatalysts. The performance of AWE depends on the catalyst's surface, interaction with water and reaction intermediates, and the formation of molecular hydrogen and oxygen. The review highlights recent advances in electrocatalysts, including the role of phase segregation, defect structures, and the e_g orbital filling in cobalt-based catalysts. It also discusses the development of new active surface species and the activation of cobalt- and nickel-based catalysts through iron uptake from the alkaline electrolyte. Challenges in large-scale production and utilization of green hydrogen are addressed, including the need for efficient, stable, and cost-effective electrocatalysts. The review emphasizes the importance of understanding the reaction mechanisms and physicochemical properties of catalysts to improve the efficiency and sustainability of AWE. The potential of new compositions and materials for enhancing energy efficiency and advancing the field of green hydrogen production is also discussed. Overall, the review underscores the critical role of AWE in the transition to a sustainable energy system and the need for continued research and development in this area.