Conventional transparent materials can be primarily divided into four categories, i.e., glasses, polymers, single crystals, and transparent ceramics. Growing large single crystals with high melting points is difficult, and glass and polymers have poor mechanical and chemical stability. These shortcomings limit their applications. Transparent ceramics are favored because of their high refractive index, high hardness, high strength, high thermal conductivity, and high chemical stability. In 2005, La2Hf2O7 was fabricated into transparent ceramics with a high density and a high atomic number, having a great potential in the detection field of scintillators. Since then, A2B2O7 transparent ceramics has attracted much attention. The structure of A2B2O7 ceramics is mainly determined by the radius ratio of A-site and B-site ions (rA/rB), and includes three structures (i.e., fluorite structure (rA/rB<1.46), pyrochlore structure (1.461.78)). While, only the fluorite- and pyrochlore-structure A2B2O7 ceramics could be transparent monolith when sintered at proper temperature and pressure.A2B2O7 ceramics with fluorite and pyrochlore two-phase coexisting structures have the advantage of smaller grains, compared with conventional A2B2O7 transparent ceramics with single-phase structures. The mechanical properties of two-phase coexisting structures ceramics can be improved due to the smaller grains. LaLuZr2O7 transparent ceramics with two phases of fluorite and pyrochlore were fabricated in 2014. Two phases are uniformly distributed in the ceramic and the average grain size of the ceramic is only 2?3μm. The in-line transmittance of LaLuZr2O7 transparent ceramic is 73.4% at 1 100 nm due to the close refractive index between the two phases of fluorite and pyrochlore, and the scattering of light across the interface between the two phases is negligible. In 2019, (La0.2Nd0.2Sm0.2Gd0.2Yb0.2)2Zr2O7 was fabricated into transparent ceramics with a fluorite and pyrochlore two-phase coexisting structure. Compared with conventional transparent ceramics, high-entropy transparent ceramics may have better mechanical properties, corrosion resistance, and high-temperature resistance. The enhanced atomic disorder due to multi-element doping in high-entropy ceramics makes it a promising material for high-temperature windows with a lower thermal conductivity. However, there are some challenges in the preparation of two-phase coexistence transparent A2B2O7 ceramics. In some previous reports on A2B2O7 transparent ceramics with two-phase coexistence, the transmittance of the ceramics was severely reduced when there was a large difference in the grain sizes of the fluorite and pyrochlore phases.It is necessary to ensure that the grain growth rates of the pyrochlore and fluorite phases are similar during sintering. Transparent ceramic scintillators of La2Hf2O7:Ti4+ were fabricated in 2005. The transmittance of La2Hf2O7:Ti4+ transparent ceramics at 600-800 nm is close to 60%. La2Hf2O7:Ti4+ transparent ceramics gain a high X-ray stopping power due to its high density and high atomic number. The integrated emission intensity of La2Hf2O7:Ti4+ transparent ceramics is 1.5 times greater than that of Bi4Ge3O12 single crystals for the same size and the same excitation conditions. In 2019, Tb2Hf2O7 was fabricated into transparent ceramics. Tb2Hf2O7 transparent ceramic ceramics perform well in the Faraday magneto-optical effect tests, having higher measured Verdet constants than commercial Tb3Ga5O12 single crystals and a potential application as an excellent magneto-optical material. It is indicated that the magneto-optical properties of magneto-optical materials are related to the concentration of Tb3+ in the materials, and the higher the Tb3+ concentration is, the better the magneto-optical properties will be. Tb2Hf2O7 transparent ceramics can be doped with higher concentrations of Tb3+ due to the structural advantages of A2B2O7, thus having better magneto-optical properties rather than garnet-structured Tb3Ga5O12 single crystal.Summary and prospects This review represented the preparation methods, performances, and potential applications of A2B2O7 transparent ceramic. A2B2O7 transparent ceramics have the characteristics of a high melting point, a high density, and a high refractive index, which are potentially valuable in the fields of optical material. However, the optical loss and optical homogeneity of A2B2O7 transparent ceramics are difficult to guarantee, a further study of optical quality improvement for A2B2O7 transparent ceramics is still needed. At present, the preparation process of A2B2O7 transparent ceramics is still immature, there are many residual pores in the sintered A2B2O7 transparent ceramics, affecting the optical quality of the A2B2O7 transparent ceramics. It is necessary to optimize the raw powder preparation process and add sintering additives to reduce the pores in the sintered A2B2O7 transparent ceramics. Although A2B2O7 transparent ceramics have great application prospects in solid-state lasers, the low thermal conductivity of A2B2O7 transparent ceramics makes heat dissipation a challenge. If A2B2O7 transparent ceramics can be used in solid-state lasers, a superior heat dissipation system needs to be designed. In summary, A2B2O7 transparent ceramics is a promising transparent material, but there are still many problems to be solved before the application.