Low (alpha)- and high-temperature (beta) forms of BiTaO4 have attracted much attention due to their dielectric and photocatalytic properties. In the present work, a third form, the so-called HP-BiTaO4, was synthesized at high temperature and pressure. The phase evolution, phase transformations, and dielectric properties of alpha- and beta-BiTaO4 and HP-BiTaO4 ceramics are studied in detail. beta-BiTaO4 ceramics densified at 1300 degrees C with the microwave permittivity epsilon(r) approximate to 53, the microwave quality factor Q(f) approximate to 12070 GHz, and the temperature coefficient of resonant frequency tau(f) approximate to -200 ppm/degrees C. HP-BiTaO4 ceramics were synthesized at 5 GPa and 1300 degrees C followed by annealing at 600 degrees C. In contrast with the alpha phase, HP-BiTaO4 exhibited epsilon(r) approximate to 195 at 1 kHz to 10 MHz, accompanied by a low dielectric loss of similar to 0.004. The relation between structure and dielectric properties is discussed in the context of Shannon's additive rule and bond theory.