Three-dimensional near-equilibrium potential energy surfaces and dipole moment functions have been calculated for the X (1) Sigma(+) ground states of NCS- and CNS-, using the coupled cluster method with single and double substitutions augmented by a perturbative estimate of triple excitations [CCSD(T)] with a set of 154 contracted Gaussian-type orbitals. The corresponding equilibrium bond lengths at their linear geometries are r(e)(NC)=1.1788 Angstrom and r(e)(CS)=1.6737 Angstrom for NCS-, and r(e)(CN)=1.1805 Angstrom and r(e)(NS)=1.6874 Angstrom for CNS-. The predicted equilibrium rotational constants B-e of NCS- and CNS- are 5918.2 and 6282.7 MHz, respectively. The former agrees very well with the known experimental value (5919.0 MHz). Full three-dimensional variational calculations have also been carried out using the CCSD(T) potential energy and dipole moment functions to determine the rovibrational energy levels and dipole moment matrix elements for both NCS- and CNS-. The corresponding fundamental band origins (cm(-1)) nu(1), nu(2), and nu(3) and their absolute intensities (km/mol) at the CCSD(T) level are 2060.9/306.1, 451.5/2.2, and 707.5/12.8, respectively, for NCS- and 2011.4/6.6, 343.7/2.3, and 624.9/0.2 for CNS-. The calculated nu(1) (CN stretching) value for NCS- is in very good agreement with the experimental result, 2065.9 cm(-1). The calculated dipole moments of NCS- and CNS- in their ground vibrational states are 1.427 and 1.347 D, respectively The transition state geometry (saddle point) for the isomerization of NCS--->CNS- is predicted at the CCSD(T) level to be r(NC)=1.2044 Angstrom, R(CS)=1.9411 Angstrom and theta(angle NCS)=86.8 degrees. Its calculated energy is 62.6 and 26.5 kcal/mol above the minima of NCS- and CNS-, respectively, including zero-point energy corrections. The structure of the NCS radical was also optimized at the same level of theory, yielding ion to neutral bond length shifts in excellent agreement with those derived from recent photoelectron spectroscopy experiments.