AASHTO GSID-4, Guide Specifications for Seismic Isolation Design, 4th Edition (2014), addresses the design of highway bridges using seismic isolation systems. The specifications begin with applicability, definitions and notation, and provisions for seismic hazard, including acceleration coefficients and site effects and site factors. Subsequent sections set out the design response spectrum, seismic zones, the response modification factor, and analysis procedures ranging from a simplified method to single mode spectral, multimode spectral, and time-history methods. Design properties of isolation systems, system property modification factors, clearances, and design forces for seismic zones 1 through 4 are specified, together with other requirements covering non-seismic lateral forces, cold weather conditions, lateral restoring force, and vertical load stability. The specifications reflect updates to corresponding provisions in Section 14 of the AASHTO LRFD Bridge Design Specifications. Bridge designers and reviewers responsible for isolated bridge structures can apply the document in seismic design work.