The photoluminescence (PL) and optically detected magnetic resonance (ODMR) spectra of poly(3-hexylthiophene) in solutions of CCl4, toluene, and CH2Cl2, and films cast from these solutions, are described and discussed. In solution, the PL yield is 7%, and increases with increasing temperature. In oxygen-free, protected films cast from these solutions, the room-temperature yield is ∼0.7%, the spectra is red shifted by ∼0.5eV, and strong peaks at 1.52, 1.69, and 1.86eV appear. In films and CH2Cl2 solutions, the ODMR is resolvable into narrow and broad components, and its intensity ΔL/L is ∼5 × l0−5 at room temperature. A strong photoinduced oxidation process quenches the PL upon exposure to O2 but not water, at a rate possibly limited by O2 diffusion.