The paper reviews the recent advancements and challenges in the field of ferromagnetism in dilute magnetic semiconductors (DMSs) and dilute magnetic oxides (DMOs). Over the past decade, significant progress has been made in understanding and controlling ferromagnetic functionalities in these materials, driven by the discovery of remarkable low-temperature functionalities in compounds like (Ga,Mn)As and p-(Cd,Mn)Te. The $p-d$ Zener model, which describes the exchange interaction between band carriers and localized spins, has been a cornerstone in explaining the thermodynamic and micromagnetic properties of DMSs. However, the origin and control of ferromagnetism in DMSs and DMOs remain highly controversial, with various models and experimental findings coexisting. The paper discusses the two main classes of ferromagnetic systems: p-type Mn-based DMSs, where ferromagnetism is associated with the presence of holes, and a broad range of semiconductors, oxides, and carbon derivatives showing ferromagnetic-like features persisting above room temperature without the need for itinerant holes. The origin of high-temperature ferromagnetism in these systems is attributed to non-random distributions of magnetic cations, which can form nanoscale regions with high spin ordering temperatures. The review also highlights the potential of ferromagnetic metal/semiconductor nanocomposites for various applications, such as magnetic field sensors, photonic devices, and all-metallic nanoelectronics. The authors emphasize the need for further research to understand the complex interplay between magnetic ion distribution, carrier correlation, and ferromagnetic properties, and to develop methods for controlling the formation and shape of magnetic nanocrystals. Overall, the paper underscores the importance of DMSs and DMOs as a platform for exploring novel functionalities and materials science, while also pointing out the remaining challenges and future directions in the field.The paper reviews the recent advancements and challenges in the field of ferromagnetism in dilute magnetic semiconductors (DMSs) and dilute magnetic oxides (DMOs). Over the past decade, significant progress has been made in understanding and controlling ferromagnetic functionalities in these materials, driven by the discovery of remarkable low-temperature functionalities in compounds like (Ga,Mn)As and p-(Cd,Mn)Te. The $p-d$ Zener model, which describes the exchange interaction between band carriers and localized spins, has been a cornerstone in explaining the thermodynamic and micromagnetic properties of DMSs. However, the origin and control of ferromagnetism in DMSs and DMOs remain highly controversial, with various models and experimental findings coexisting. The paper discusses the two main classes of ferromagnetic systems: p-type Mn-based DMSs, where ferromagnetism is associated with the presence of holes, and a broad range of semiconductors, oxides, and carbon derivatives showing ferromagnetic-like features persisting above room temperature without the need for itinerant holes. The origin of high-temperature ferromagnetism in these systems is attributed to non-random distributions of magnetic cations, which can form nanoscale regions with high spin ordering temperatures. The review also highlights the potential of ferromagnetic metal/semiconductor nanocomposites for various applications, such as magnetic field sensors, photonic devices, and all-metallic nanoelectronics. The authors emphasize the need for further research to understand the complex interplay between magnetic ion distribution, carrier correlation, and ferromagnetic properties, and to develop methods for controlling the formation and shape of magnetic nanocrystals. Overall, the paper underscores the importance of DMSs and DMOs as a platform for exploring novel functionalities and materials science, while also pointing out the remaining challenges and future directions in the field.