Perchloryl fluoride, FClO3, has been Studied both experimentally and theoretically, using high-resolution Fourier transform spectroscopy and high-level ab initio methods. The geometry, dipole moment, and anharmonic force field of the molecule have been calculated ab initio, using the coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)] level of theory. The infrared spectra of monoisotopic species have been recorded. The v(1) + v(1) bands of (FClO3)-Cl-35-O-16, (FClO3)-Cl-37-O-18, and (FClO3)-Cl-37-O-18, v(2) + v(3) and v(2) + v(3) - v(3) bands of (FClO3)-Cl-35-O-16 and (FClO3)-Cl-31-O-16, and the 2v(3) - v(3) band of (FClO3)-Cl-37-O-16 have been analyzed. The spectroscopic parameters obtained from these and from previous analyses have been compared with the theoretical results.