Allyl nitrite, O=NOCH(2)CH=CH(2), can exist in conformations which include syn (S) and anti (A) configurations of O=N-O-C, anti or gauche (G) configurations of N-O-C-C, and syn or skew (Sk) configurations of O-C-C=C. Four of them have been observed and characterized by their microwave spectra and quantum chemical calculations to have AGSk' (0.0 kcal/mol), AGSk (0.2(2) kcal/mol), SASk (0.2(2) kcal/mol), and SAS (0.9(2) kcal/mol) configurations about the three successive dihedral angles. All four are observed in microwave studies of the vapor at 300 and 200 K and the first three are seen in pulsed-jet beams. The SAS form apparently relaxes to the SASk conformer during expansion in the pulsed-jet. Quantum chemical calculations reveal that the two possible conformers with anti-anti configurations of the O=N-O-C-C fragment, AAS and AASk, are transition states, unstable configurations, or of marginal stability, consistent with structures observed in this and other previously studied alkyl nitrites. The remaining four possible conformers are predicted to have relative energies within 1 kcal/mol of the observed conformers but were not observed experimentally.