The structural and electronic properties of pyridine, its oligomers, and polypyridine (PPY) as obtained with density functional methods are presented in this work. Among the different exchange-correlation functionals used, B3LYP,gives good structural results, whereas B3P88 predicts more accurately the electronic properties. The calculated first excitation energies of pyridine systems are in good agreement with experimental data. The coupling between the monomers in forming oligomers influences the structural and electronic properties of the system significantly, The trans head-to-head dimer is found to be the most stable form and the only one having a planar geometry. The introduction of a head-to-head or tail-to-tail coupling in order to break the regioregularity of a tetramer changes the frontier orbitals and the total energy of the system. The inclusion of a head-to-head coupling in the central units of a tetramer leads to a global stabilization of the system and lowers the HOMO, producing an increase in the first electronic excitation energy. Finally, the electronic properties of infinite PPY are obtained by extrapolations from those of finite oligomers, The calculated ionization potential, electronic affinity, and (pi-pi)(1) transition are 6.3, 3.4, and 2.9 eV, respectively, in excellent agreement with previous experimental reports. Furthermore, the band structures and density of states of PPY are calculated using a DFT-LMTO method. The calculated density of states is in good qualitative and quantitative agreement with experimental UPS spectrum for this system.