Absorption spectra between 0.2 and 6.7 μm are reported for trivalent samarium in single-crystal yttrium aluminum garnet, Y 3Al 5O 12, at liquid-helium, liquid-nitrogen, and room temperatures. Energy levels (4f 5[ SL] Jμ) associated with sextet, quartet, and doublet states of Sm 3+ are established from data between 1500 and 46000 cm −1. Most samarium ions occupy yttrium ion sites, which have D 2 point-group symmetry in the lattice. A free-ion wavefunction calculation predicts the assignment of 35 isolated [ SL] J manifolds with an rms deviation of 32 cm −1 between calculated and observed centers of gravity. A hamiltonian consisting of coulombic, spin—orbit, and crystalline electric field (D 2 symmetry) terms is diagonalized for the two lowest sextet states [6H] J and [6F] J. The calculated Stark levels based on a single set of B km crystal field parameters are compared to the observed levels (54) yielding an rms deviation of 4.9 cm −1.