The article reviews the theory of ferromagnetic (III,Mn)V diluted magnetic semiconductors (DMSs), focusing on their fundamental physics, materials science, and spintronic applications. It discusses the origins of ferromagnetism in these materials, emphasizing the role of Mn impurities and their interactions with itinerant electrons. The review highlights the importance of growth techniques in achieving high-quality (III,Mn)V DMSs and their magnetic properties. It also addresses the challenge of increasing Curie temperatures to room temperature for practical applications. The article covers various theoretical approaches, including first-principles calculations, tight-binding models, and effective Hamiltonian theories, to understand the magnetic and electronic properties of (III,Mn)V DMSs. It discusses the structural and magnetic properties of these materials, as well as their magneto-transport and magneto-optical characteristics. The review also explores the potential of (III,Mn)V DMSs in spintronics, including their use in spintronic devices and the development of new functionalities. The article concludes with a discussion on the future prospects of (III,Mn)V DMSs in achieving high-temperature ferromagnetism and their potential applications in microelectronics.The article reviews the theory of ferromagnetic (III,Mn)V diluted magnetic semiconductors (DMSs), focusing on their fundamental physics, materials science, and spintronic applications. It discusses the origins of ferromagnetism in these materials, emphasizing the role of Mn impurities and their interactions with itinerant electrons. The review highlights the importance of growth techniques in achieving high-quality (III,Mn)V DMSs and their magnetic properties. It also addresses the challenge of increasing Curie temperatures to room temperature for practical applications. The article covers various theoretical approaches, including first-principles calculations, tight-binding models, and effective Hamiltonian theories, to understand the magnetic and electronic properties of (III,Mn)V DMSs. It discusses the structural and magnetic properties of these materials, as well as their magneto-transport and magneto-optical characteristics. The review also explores the potential of (III,Mn)V DMSs in spintronics, including their use in spintronic devices and the development of new functionalities. The article concludes with a discussion on the future prospects of (III,Mn)V DMSs in achieving high-temperature ferromagnetism and their potential applications in microelectronics.