The article "Classifying multiferroics: Mechanisms and effects" by Daniel Khomskii provides an overview of the field of multiferroics, which has seen significant expansion in recent years. Multiferroics are materials that exhibit both ferroelectric and ferromagnetic properties, coexisting in the absence of external fields. The review organizes these materials based on the microscopic mechanisms that govern their properties and explores the potential for finding similar multiferroic behavior in various systems. The history of multiferroics is traced back to the 19th century, with early predictions of piezomagnetism and linear coupling between magnetic and electric fields. The field gained momentum in the 21st century with the discovery of new multiferroic materials and the realization of strong coupling between magnetism and ferroelectricity. Key milestones include the successful growth of thin films of BiFeO₃ and the discovery of materials like TbMnO₃ and TbMn₂O₅, where magnetism causes ferroelectricity. The article classifies multiferroics into two main groups: type-I and type-II. Type-I multiferroics have ferroelectricity and magnetism with different sources, while type-II multiferroics exhibit strong coupling between the two. Type-I multiferroics include perovskites, materials with lone pairs, charge ordering, and geometric ferroelectricity. Type-II multiferroics are further divided into those with magnetic spirals and those with collinear magnetic structures, both of which can induce ferroelectricity through various mechanisms. The review also discusses the practical applications of multiferroics, such as electric control of magnetic memory and the creation of new types of logic states. It highlights the importance of understanding the basic physics and the potential for "multiferroics by design" through advanced computational methods. The field is expected to continue evolving, with ongoing research focusing on the discovery of new materials, the exploration of dynamical properties, and the development of artificial composite multiferroics. Overall, the article underscores the rich physics and promising applications of multiferroics, emphasizing the active and dynamic nature of the field.The article "Classifying multiferroics: Mechanisms and effects" by Daniel Khomskii provides an overview of the field of multiferroics, which has seen significant expansion in recent years. Multiferroics are materials that exhibit both ferroelectric and ferromagnetic properties, coexisting in the absence of external fields. The review organizes these materials based on the microscopic mechanisms that govern their properties and explores the potential for finding similar multiferroic behavior in various systems. The history of multiferroics is traced back to the 19th century, with early predictions of piezomagnetism and linear coupling between magnetic and electric fields. The field gained momentum in the 21st century with the discovery of new multiferroic materials and the realization of strong coupling between magnetism and ferroelectricity. Key milestones include the successful growth of thin films of BiFeO₃ and the discovery of materials like TbMnO₃ and TbMn₂O₅, where magnetism causes ferroelectricity. The article classifies multiferroics into two main groups: type-I and type-II. Type-I multiferroics have ferroelectricity and magnetism with different sources, while type-II multiferroics exhibit strong coupling between the two. Type-I multiferroics include perovskites, materials with lone pairs, charge ordering, and geometric ferroelectricity. Type-II multiferroics are further divided into those with magnetic spirals and those with collinear magnetic structures, both of which can induce ferroelectricity through various mechanisms. The review also discusses the practical applications of multiferroics, such as electric control of magnetic memory and the creation of new types of logic states. It highlights the importance of understanding the basic physics and the potential for "multiferroics by design" through advanced computational methods. The field is expected to continue evolving, with ongoing research focusing on the discovery of new materials, the exploration of dynamical properties, and the development of artificial composite multiferroics. Overall, the article underscores the rich physics and promising applications of multiferroics, emphasizing the active and dynamic nature of the field.