Transparent amorphous oxide semiconductors (AOSs) have unique electron transport properties, such as high electron mobility (10–50 cm²/Vs) and the absence of Hall voltage sign anomalies, which are not observed in conventional amorphous semiconductors. These materials have gained significant attention for their use in thin-film transistors (TFTs) due to their processing advantages, such as low-temperature deposition using conventional sputtering methods. The primary driving force behind this trend is the emerging demand for backplane TFTs that can drive next-generation flat-panel displays. This article reviews recent advances in the fundamental science of AOS materials and their applications in TFTs. It highlights the role of high ionicity in chemical bonding and the large spherical spread of unoccupied metal s orbitals in p-block metal oxides, which lead to advantageous electronic structures for n-channel TFT applications. AOSs are compared with conventional hydrogenated amorphous silicon (a-Si:H), which is widely used in current liquid-crystal displays. The article also discusses the advantages of AOS TFTs, including low processing temperatures, ease of fabrication, and superior carrier transport properties. It reviews the history of AOS development, the materials and processes involved, and the electronic structures that explain the unique properties of AOSs. Finally, it addresses current and future issues in AOS technology, such as long-term stability, photoresponse, and the need for mass-production compatible methods.Transparent amorphous oxide semiconductors (AOSs) have unique electron transport properties, such as high electron mobility (10–50 cm²/Vs) and the absence of Hall voltage sign anomalies, which are not observed in conventional amorphous semiconductors. These materials have gained significant attention for their use in thin-film transistors (TFTs) due to their processing advantages, such as low-temperature deposition using conventional sputtering methods. The primary driving force behind this trend is the emerging demand for backplane TFTs that can drive next-generation flat-panel displays. This article reviews recent advances in the fundamental science of AOS materials and their applications in TFTs. It highlights the role of high ionicity in chemical bonding and the large spherical spread of unoccupied metal s orbitals in p-block metal oxides, which lead to advantageous electronic structures for n-channel TFT applications. AOSs are compared with conventional hydrogenated amorphous silicon (a-Si:H), which is widely used in current liquid-crystal displays. The article also discusses the advantages of AOS TFTs, including low processing temperatures, ease of fabrication, and superior carrier transport properties. It reviews the history of AOS development, the materials and processes involved, and the electronic structures that explain the unique properties of AOSs. Finally, it addresses current and future issues in AOS technology, such as long-term stability, photoresponse, and the need for mass-production compatible methods.