The unusual spectra of the spatially-resolved nova shells of DQ Her, T Aur and CP Pup are reviewed. Because calculations for these conditions have not been made, recombination models of HI, HeI and CNO from a neutral to a doubly ionized state were constructed. The models are described and the results presented for densities at various temperatures. A photoionization model is also described. The effects of non-uniform density distributions in nova shells have been investigated and the observational consequences discussed. A model of the CP Pup shell is described and the evolution of this plasma during the nova's constant luminosity phase traced. The properties of neon novae are summarized and compared with the features seen in the optical spectra of old classical novae. Enhanced neon abundances are used in the model of the CP Pup Shell to investigate its effect on the evolution of the shell. Finally, the results of some near-infrared observations made on the shells of CP Pup, RR Pic and T Pyx are reported.

Bibliography: pages 155-165.