This focus review provides a comprehensive overview of high-entropy oxides (HEOs), highlighting their unique properties and potential applications. HEMs, which are crystalline, phase-pure, and configurationally disordered materials containing at least five elements evenly blended into a solid-solution framework, have revolutionized materials science by offering new avenues for material exploration, property optimization, and advanced applications. The review emphasizes the crystal structure and functional properties of HEOs, discussing recent synthetic advances and their applications in electrocatalysis and batteries. It also addresses the challenges and constraints in HEOs, the use of theoretical and experimental tools to overcome these challenges, and potential directions for future research in energy applications. The review begins by explaining the concept of high entropy, including the thermodynamic and kinetic parameters that govern the behavior of HEMs. It discusses the role of configurational entropy in stabilizing multiple elements within a single crystal lattice, the dynamics of slow diffusion, and the "cocktail effect" where the emergent properties of HEMs cannot be attributed solely to their individual components. The review then delves into the synthesis and crystal structure of HEOs, detailing various methods such as carbothermal shock, spray pyrolysis, mechanochemistry, and colloidal chemistry. It highlights the importance of precise control over synthesis parameters to achieve single-phase HEOs and the challenges associated with these methods. Recent innovations in the synthesis and crystal structure of HEOs are discussed, including the use of molecular precursors, high-throughput characterization techniques, and the exploration of different crystal structures. The review also examines the surface performance and stability of HEOs, particularly in organic photocatalysis and catalytic applications. Finally, it concludes by discussing the advanced fundamental understanding and experimental and computational breakthroughs that can address the pressing needs in HEOs, while anticipating their impact in prospective applications.This focus review provides a comprehensive overview of high-entropy oxides (HEOs), highlighting their unique properties and potential applications. HEMs, which are crystalline, phase-pure, and configurationally disordered materials containing at least five elements evenly blended into a solid-solution framework, have revolutionized materials science by offering new avenues for material exploration, property optimization, and advanced applications. The review emphasizes the crystal structure and functional properties of HEOs, discussing recent synthetic advances and their applications in electrocatalysis and batteries. It also addresses the challenges and constraints in HEOs, the use of theoretical and experimental tools to overcome these challenges, and potential directions for future research in energy applications. The review begins by explaining the concept of high entropy, including the thermodynamic and kinetic parameters that govern the behavior of HEMs. It discusses the role of configurational entropy in stabilizing multiple elements within a single crystal lattice, the dynamics of slow diffusion, and the "cocktail effect" where the emergent properties of HEMs cannot be attributed solely to their individual components. The review then delves into the synthesis and crystal structure of HEOs, detailing various methods such as carbothermal shock, spray pyrolysis, mechanochemistry, and colloidal chemistry. It highlights the importance of precise control over synthesis parameters to achieve single-phase HEOs and the challenges associated with these methods. Recent innovations in the synthesis and crystal structure of HEOs are discussed, including the use of molecular precursors, high-throughput characterization techniques, and the exploration of different crystal structures. The review also examines the surface performance and stability of HEOs, particularly in organic photocatalysis and catalytic applications. Finally, it concludes by discussing the advanced fundamental understanding and experimental and computational breakthroughs that can address the pressing needs in HEOs, while anticipating their impact in prospective applications.