FHWA has issued earthquake design guidelines for new structures and for retrofitting. These guidelines follow the recent work product, published in October 1981, of the study done by the Applied Technology Council. Effective March 1, 1983, AASHTO has similarly adopted these criteria. Because this represents an area of design with few successful precedents and these guidelines are intended to encourage innovative thinking, this discussion will cover the following subject areas:(a) an introduction to the seismic design problem encompassing some of the fundamentals of what is known about earthquakes and their prediction,(b) examples of how structures are affected by mild and medium earthquakes,(c) the controlled base isolation concept, and (d) some of the design principles necessary for successful expansion joint and bearing performance during a typical earthquake. Some of the new tools and concepts that could be useful in seismic design are described together with their performance criteria and the testing accomplished to date to verify their performance along with design parameters for their use.