High-entropy oxides (HEOs) are a class of materials with five or more elements, characterized by high configurational entropy and phase purity. This review discusses the fundamentals, synthesis, and applications of HEOs, highlighting their potential in energy-related processes such as catalysis and battery technology. HEOs are synthesized through various methods, including high-temperature solid-state reactions, colloidal chemistry, and electrospinning, leading to diverse crystal structures like spinel, perovskite, and fluorite. The unique properties of HEOs, such as high entropy, lattice distortion, and the "cocktail effect," enable them to exhibit enhanced electrochemical activity and catalytic performance. The review also addresses the challenges in synthesizing and characterizing HEOs, emphasizing the need for further research to optimize their properties for various applications. Recent studies have demonstrated the potential of HEOs in organic photocatalysis and as efficient catalysts for reactions like CO2 hydrogenation. The review concludes with a discussion on the future directions of HEO research, focusing on improving their stability, performance, and applicability in energy technologies.High-entropy oxides (HEOs) are a class of materials with five or more elements, characterized by high configurational entropy and phase purity. This review discusses the fundamentals, synthesis, and applications of HEOs, highlighting their potential in energy-related processes such as catalysis and battery technology. HEOs are synthesized through various methods, including high-temperature solid-state reactions, colloidal chemistry, and electrospinning, leading to diverse crystal structures like spinel, perovskite, and fluorite. The unique properties of HEOs, such as high entropy, lattice distortion, and the "cocktail effect," enable them to exhibit enhanced electrochemical activity and catalytic performance. The review also addresses the challenges in synthesizing and characterizing HEOs, emphasizing the need for further research to optimize their properties for various applications. Recent studies have demonstrated the potential of HEOs in organic photocatalysis and as efficient catalysts for reactions like CO2 hydrogenation. The review concludes with a discussion on the future directions of HEO research, focusing on improving their stability, performance, and applicability in energy technologies.