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Abundance measurements of C, N, O, Ne, S, and Ar in galactic and extragalactic H II regions, planetary nebulae, and supernova remnants represent a major source of information about elemental levels in the interstellar media of spiral disks. Measured from the ground in most cases, the strengths of the numerous emission features produced by these objects can be converted in a straightforward way to ionic and elemental abundances. When the abundances for nebular objects within a single galaxy are compiled, several correlations are shown to exist either between interstellar metallicity and galactocentric distance, i.e. an abundance gradient, or between pairs of abundance ratios. Since the former is directly linked to matter distribution and star formation rates, and the latter depends on the IMF and stellar yields, complete abundance profile information for a galactic disk provides important constraints on galactic chemical evolution models and hence our global understanding of how elemental composition changes within a galaxy as a function of time and location. The purpose of this review is to provide a summary of extant data pertaining to nebular abundance profiles in disk galaxies along with brief interpretations. Readers are referred to other papers in this volume for more detailed theoretical explorations of abundance gradients.