For the past several years, our group has pursued a vigorous ground-based program aimed at understanding the nature of ultraluminous infrared galaxies. We recently published the results from a optical/near-infrared spectroscopic survey of a large statistically complete sample of ultraluminous infrared galaxies (the IRAS 1-Jy sample). We now present the results from our recently completed optical/near-infrared imaging survey of the 1-Jy sample. These data provide detailed morphological information on both large scale (e.g., intensity and color profiles, intensity and size of tidal tails and bridges, etc) and small scale (e.g., nuclear separation, presence of bars, etc) that helps us constrain the initial conditions necessary to produce galaxies with such high level of star formation and/or AGN activity. The nature of the interdependence between some key spectroscopic and morphological parameters in our objects (e.g., dominant energy source: super-starburst versus quasar, nuclear separation, merger phase, star formation rate, and infrared luminosity and color) is used to clarify the connection between starbursts, ultraluminous infrared galaxies, and quasars.
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