We present experimental infrared spectra and theoretical electronic structure results for the geometry, anharmonic vibrational frequencies, and accurate estimates of the magnitude and the origin of the ring-puckering barrier in C4F8. High-resolution (0.0015 cm(-1)) spectra of the nu(12) and nu(13) parallel bands of perfluorocyclobutane (c-C4F8) were recorded for the first time by expanding a 10% c-C4F8 in helium mixture in a supersonic jet. Both bands are observed to be rotationally resolved in a jet with a rotational temperature of 15 K. The nu(12) mode has b(2) symmetry under D-2d that correlates to a(2u), symmetry under D-4h and consequently has +/-<-+/- ring-puckering selection rules. A rigid rotor fit of the nu(12) band yields the origin at 1292.56031(2) cm I with B ' = 0.0354137(3) cm(-1) and B '' = 0.0354363(3) cm(-1). The nu(13) mode is of b(2) symmetry under D-2d that correlates to b(2g) under D-4h, and in this case, the ring-puckering selection rules are +/-<--/+. Rotational transitions from the ground and first excited torsional states will be separated by the torsional splitting in the around and excited vibrational states, and indeed, we observe a splitting of each transition into strong and weak intensity components with a separation of approximately 0.0018 cm(-1). The strong and weak sets of transitions were fit separately again using a rigid rotor model to give nu 13(strong) = 1240.34858(4) cm(-1), B ' = 0.0354192(7) cm(-1), and B '' = 0.0354355(7) cm(-1) and nu(13)(weak) = 1240.34674(5) cm(-1), B ' = 0.0354188(9) cm-1, and B '' = 0.0354360(7) cm(-1). High-level electronic structure calculations at the MP2 and CCSD(T) levels of theory with the family of correlation consistent basis sets of quadruple-zeta quality, developed by Dunning and co-workers, yield best estimates for the vibrationally averaged structural parameters r(C-C) = 1.568 angstrom, r(C-F)alpha = 1.340 angstrom, r(C-F)beta = 1.329 angstrom alpha(F-C-F) = 110.3 degrees, theta(z)(C-C-C) = 89.1 degrees, and delta(C-C-C-C) = 14.6 degrees and rotational constants of A = B = 0.03543 cm(-1) and C = 0.02898 cm(-1), the latter within 0.00002 cm(-1) from the experimentally determined values. Anhannonic vibrational frequencies computed using higher energy derivatives at the MP2 level of theory are all within < 27 cm(-1) (in most cases < 5 cm(-1)) from the experimentally measured fundamentals. Our best estimate for the ring-puckering barrier at the CCSD(T)/CBS (complete basis set) limit is 132 cm(-1). Analysis of the C4F8 electron density suggests that the puckering barrier arises principally from the sigma(cc ->)sigma(cF)* hyperconjugative interactions that are more strongly stabilizing in the puckered than in the planar form. These interactions are, however, somewhat weaker in C4F8 than in C4H8, a fact that is consistent with the smaller in the former (132 cm(-1)) with respect to the latter (498 cm(-1)).