Various theoretical methods (HF, MP2, B3-LYP, QCSD, CCSD(T)) in combination with a hierarchy of basis sets have been used to determine the ground state conformations of B2F4 and B2F4+. It was found that the ground state of B2F4 has an eclipsed conformation (in D-2h symmetry), while that of B2F4+ has a staggered conformation (in D-2d symmetry). The experimental value for the ionization potential (IP) of B2F4 was found to have a far larger error than believed. I The theoretical value of IP obtained by extrapolating the calculated energies to complete basis set limit, corrected for zero-point vibrational energy, spin-orbit and core-valence effects, is, 271.70 kcal mol(-1). Our best atomization energy and heats of formation at 0 and 298 K for the neutral B2F4 (D-2h) are 685.64 kcal mol(-1), -339.34 kcal mol(-1), and -339.82 kcal mol(-1), respectively, and those for the radical cation B2F4+ (D-2d) are 413.94 kcal mol(-1), -67.64 kcal mol(-1), and -67.72 kcal mol(-1), respectively.