We present new calculations for transition probabilities of FeIV, with much more extensive datasets than heretofore available, for a variety of astrophysical applications. The large-scale close coupling R-matrix calculations yield 1798 LS bound states with n<=11 and l<=9, and corresponding 138121 dipole allowed transitions in the form of oscillator strengths f, line strengths S, and A-coefficients. This represents the largest R-matrix dataset in LS coupling for any ion under either the Opacity Project or the Iron Project. Through algebraic transformation of the LS multiplets, a total of 712120 dipole allowed fine structure transitions for FeIV are obtained. Observed transition energies, whenever available, are used together with the energy independent line strengths to derive the f- and the A-values for improved accuracy; the adopted algorithm used calculated energies for the remainder. Present results show significantly better accuracy for the important low-lying states than previous calculations. Monochromatic and mean opacities for FeIV are computed and compared with those obtained using the Opacity Project data. We find differences which could have important consequences for several astrophysical applications involving low ionization stages of iron.