Compared with the seismic performance of concrete and steel highway bridges, the seismic performance of timber bridges is not well understood. This is because, historically, little effort has been spent on documenting the seismic performance of timber bridges in past earthquakes or conducting research to develop an improved understanding of the seismic design or retrofit requirements for timber bridges. Research work sponsored by FHWA and conducted at the University at Buffalo in conjunction with the Multidisciplinary Center for Earthquake Engineering Research to ( a) document the seismic performance of timber bridges in past earthquakes, ( b) experimentally assess the strength and ductility capabilities of timber pile substructures, and ( c) conduct a seismic vulnerability analysis of timber bridges (principally with shaking in the longitudinal direction) to assess the expected modes of failure is presented. Finally, with a particular emphasis on the 1964 Alaska earthquake, conclusions demonstrating why certain types of behavior lead to failures in timber bridges are drawn.