The spectrum of singly-ionized iron (Fe II) has been recorded using high-resolution Fourier transform and grating spectroscopy over the wavelength range 900 Å to 5.5 μm. The spectra were recorded in high-current continuous and pulsed hollow cathode discharges using Fourier transform (FT) spectrometers at the National Solar Observatory, Tucson, AZ and Imperial College, London and with the 10.7 m Normal Incidence Spectrograph at the National Institute of Standards and Technology. Roughly 12 900 lines were classified using 1028 energy levels of Fe II that were optimized to measured wavenumbers. The wavenumber uncertainties of lines in the FT spectra range from 10−4 cm−1 for strong lines around 4 μm to 0.05 cm−1 for weaker lines around 1500 Å. The wavelength uncertainty of lines in the grating spectra is 0.002 Å for moderately strong lines that do not saturate the photographic plate. The ionization energy of 130655.4±0.4 cm−1 was estimated from the 3d6(5D)5g and 3d6(5D)6h levels.