This report summarizes the principal findings of a four year study for Caltrans of the seismic response of older multi-level, multi-column reinforced concrete bridge structures. Methods have been devised to improve prediction of the global response of these structures, to analyze and assess their local behavior, and to retrofit them to achieve adequate seismic behavior. The behavior of these structures has been found to be complex and influenced by a wide variety of parameters. Moreover, existing analysis methods often provide non-conservative estimates of behavior. The investigations conducted provide greater insight into the response characteristics of existing multiple column bridge structures. These have permitted development of improved analytical models and tools, retrofit strategies and design concepts.