This is the first in a series of STRUCTURE® articles that have been condensed and adapted from the Structural Engineers Association of California (SEAOC) online series called the SEAOC Blue Book: Seismic Design Recommendations. Beginning in 1959 and extending to 1996, the SEAOC Seismology Committee published updated printed editions of Recommended Lateral Force Requirements and Commentary, which was commonly called the Blue Book. The "Requirements" portion of those publications was in large part adopted verbatim by the International Council of Building Officials as the seismic regulations of the Uniform Building Code. With the transition to the unification of the three major model building code organizations into the International Code Council, and the nationwide use of the NEHRP seismic design provisions that are developed under the auspices of FEMA and the Building Seismic Safety Council, SEAOC decided the "Requirements" portion of the Blue Book no longer served a purpose, but that there was a still a need for statements of position and guidance for practicing engineers and code officials to help them to resolve ambiguities among various codes and standards and to interpret research. A number of Blue Book articles are in development and are being published one-by-one, after each has passed through an extensive SEAOC Seismology Committee review process.