The microwave spectra of CH3CH2SnH3 and CH3CH2SnD3 for the five most abundant isotopes of naturally occurring tin, 116Sn, 117Sn, 118Sn, 119Sn, and 120Sn, have been recorded in the range 18.0–40.0 GHz. Only a-type transitions were identified and R-branch assignments have been made for the ground vibrational state. The components of the dipole moment were determined from the Stark effect to be ‖μa‖=0.86±0.01 D, ‖μb‖=0.48±0.04 D, and ‖μt‖=0.99±0.02 D. No splittings in the ground state were observed due to the internal rotation of either the SnH3 or CH3 tops. Based on this observation, lower limits to the barriers to internal rotation of 1.12 and 2.12 kcal/mol are estimated for the SnH3 and CH3 tops, respectively. The following five structural parameters were determined from a least-squares fit of the 20 rotational constants (B and C only): r(Sn–C)=2.143±0.003 Å; r(C–C) =1.552±0.025 Å; ∢HSnC=109.5±0.1°; ∢HCH=107.5±3.9°; ∢SnCC=112.6±0.9°. The Raman spectra (3200–10 cm−1) were obtained for all three phases and infrared spectra (3200–80 cm−1) were obtained for the gas and solid. An assignment is proposed based on band contours, depolarization values, isotopic shifts, and group frequencies for all the normal modes except the two internal torsions; however, the methyl torsion in CH3CH2SnD3 has been tentatively assigned to a band observed at 242 cm−1 in the infrared spectrum of the solid. A normal coordinate calculation was carried out by utilizing a modified valence force field with 30 internal coordinates and 21 force constants. The observed frequencies are fit to better than 1%. The observed splitting of the normal modes in the spectra of the solids along with the number of observed lattice modes is consistent with two molecules per primitive cell. The results are compared to corresponding quantities in some similar molecules.