This work describes and discusses Photoluminescence (PL), and X-band Photoluminescence Detected Magnetic Resonance (PLDMR) of poly(3-alkylthiophene) (P3AT) films and solutions, poly(para-phenylenevinylene) (PPV), poly(2,5-dihexoxyparaphenylenevinylene) (PDHOPV), poly(2,5-dioctoxyparaphenylenevinylene) (PDOOPV), blends of poly(2-methoxy,5-(2[superscript]'ethylhexoxy)paraphenylenevinylene) (PMOEHOPV) with polyethylene (PE) films both unoriented and oriented, and poly(2,5-dibutoxyparaphenyleneacetylene) (PDBOPA) films. The Electroluminescence Detected Magnetic Resonance (ELDMR) and Conductivity Detected Magnetic Resonance (CDMR) narrow quenching signal in PPV is also reported and discussed.;The PLDMR of all polymers exhibit the following PL enhancing features: (i) a narrow resonance at g ≅ 2.003, (ii) a broad triplet powder pattern around g ~ 2, and (iii) the [delta]m[subscript] s = 2 transition of this triplet at g ≅ 4.07. In P3AT and thermally cycled PPV derivatives, a broad PL-quenching resonance is present around g ~ 2. The narrow resonance, symmetric in PPV, PDHOPV, PDOOPV, and PDBOPA but not in P3AT, is attributed to "distant" polaron recombination, indicating charge conjugation symmetry violation is stronger in the latter system. The spectral dependance of the narrow resonance in P3AT, PPV and PDHOPV which is similar to the PL spectrums suggests that the polaron levels are close to the band edges. Two distinct excitons are observed in P3AT at low and high temperatures. The low temperature exciton is suspected to be weakly pinned to the thiophene rings. The high temperature exciton, observed in all polymer films and powders measured except PPA, which has different symmetry, is believed to be a mobile intrinsic feature in nondegenerate ground state (semi)conducting polymers. PPA is an exception probably due to a high degree of disorder in the samples studied. A broad PL-quenching PLDMR about g ~ 2, is observed in P3HT and PDHOPV at low temperature, probably due to geminate singlet decay. Its FWHM of 300 G, assuming a lifetime broadened resonance, correlates with measured PL lifetimes of ~400 ps.;ELDMR measurements on PPV also yielded an enhancing half field triplet powder pattern similar to that observed in the PLDMR. However, a much stronger narrow EL-quenching resonance is observed at g ≅ 2.0023, probably due to non-radiative decay of two like charged polarons to a bipolaron. The narrow conductivity-quenching CDMR is attributed to the same decay channel, as the mobility of a bipolaron is believed to be lower than that of a polaron.