This paper presents an ab initio study of the spontaneous polarization, piezoelectric constants, and dynamical charges of III-V nitride semiconductors AlN, GaN, and InN using the Berry phase approach. The results show that III-V nitrides exhibit properties similar to II-VI oxides and ferroelectric perovskites. The piezoelectric constants of these nitrides are up to 10 times larger than those of conventional III-V and II-VI materials and comparable to those of ZnO. The spontaneous polarization is very large, with AlN having the largest value reported so far for any binary compound, and only about 3-5 times smaller than in typical ferroelectric perovskites. The piezoelectric constants have the same sign as in II-VI compounds and opposite to III-V compounds. The Born effective charges in the nitrides are within 10% of the nominal ionic charge, indicating a high ionic character. The results also show that the nitrides follow a well-defined III-V trend in their piezoelectric constants, with the constants increasing in magnitude as the anion becomes lighter. The study also compares the properties of wurtzite and zincblende structures, showing that the nitrides have a unique combination of properties that distinguish them from conventional III-V semiconductors. The calculated values of spontaneous polarization and piezoelectric constants are in good agreement with experimental data for AlN. The results have important implications for the design and application of nitride-based piezoelectric devices and multilayer structures.This paper presents an ab initio study of the spontaneous polarization, piezoelectric constants, and dynamical charges of III-V nitride semiconductors AlN, GaN, and InN using the Berry phase approach. The results show that III-V nitrides exhibit properties similar to II-VI oxides and ferroelectric perovskites. The piezoelectric constants of these nitrides are up to 10 times larger than those of conventional III-V and II-VI materials and comparable to those of ZnO. The spontaneous polarization is very large, with AlN having the largest value reported so far for any binary compound, and only about 3-5 times smaller than in typical ferroelectric perovskites. The piezoelectric constants have the same sign as in II-VI compounds and opposite to III-V compounds. The Born effective charges in the nitrides are within 10% of the nominal ionic charge, indicating a high ionic character. The results also show that the nitrides follow a well-defined III-V trend in their piezoelectric constants, with the constants increasing in magnitude as the anion becomes lighter. The study also compares the properties of wurtzite and zincblende structures, showing that the nitrides have a unique combination of properties that distinguish them from conventional III-V semiconductors. The calculated values of spontaneous polarization and piezoelectric constants are in good agreement with experimental data for AlN. The results have important implications for the design and application of nitride-based piezoelectric devices and multilayer structures.