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Infrared observations of classical novae have established their importance as laboratories for studying astrophysical grain formation, and as contributors to abundance anomalies in the interstellar medium. Studies of abundances in nova ejecta also provide information about nucleosynthesis in the white dwarf progenitor and in the thermonuclear runaway during a nova explosion. Two key, virtually unexplored problems that our proposed ISO investigations will address are the documentation of the detailed spectral energy distributions and the temporal characteristics of classical novae at wavelengths greater than 20 microns. Examination of the IRAS database shows that a number of old novae are anomalously bright at 25, 60, and 100 microns. This wavelength regime contains many forbidden lines from heavy elements that are useful for excitation and abundance studies. Continuum emission and broad emission features at these wavelengths give information about dust grains. In contrast to the Central Program nova observations, the proposed source list overlaps heavily with the IRAS database, so that the nature of the IRAS detections can be deduced. Our choice of objects and scientific problems is designed to produce an understanding of fundamental differences between evolved CO and ONeMg novae. Specifically, our proposed ISO initiative seeks to address four research problems in the study of classical nova evolution: 1) chemical abundances of nova ejecta from coronal and forbidden emission line spectroscopy; 2) frequency of the occurrence of ONeMg novae from observations of the emission lines in the ejecta of old IRAS novae; 3) grain size distribution and mineral composition of nova dust; and 4) dynamical studies of nova ejecta. The criteria imposed by our science objectives in these areas require us to obtain ISO observations of novae not contained in the ISO Central Program.