An experimental study investigated retrofitting measures for improving the seismic performance of the foundations of existing bridges. Retrofit measures for both pile-supported and spread footings were investigated. Tests were conducted on 1/3-scale footing and column assemblages that incorporated details selected to represent deficiencies common in older bridges. Tests on the as-built specimens resulted in a brittle failure because of insufficient joint shear strength in the column-footing connection. An added reinforced concrete overlay provided an effective retrofit for the as-built footings. In specimens that were overturning critical, increased overturning resistance was achieved by enlarging the footing plan size, by providing additional piles, or by providing tie-downs through the footing.