Since the introduction of response spectrum technique in earthquake resistant design of structures(32-18), considerable progress has been made in the earthquake regulations of the world to include, in one form or the other, the dynamic properties of earthquakes as well as those of the structures. Important differences, however, still exist in the approach for determining the seismic coefficients for design not only from one code to the other in different countries(), but from region to region or organisation to organisation within the same country() and from one structure to the other in the same codet1?) also. Usually base seismic coefficients are specified for different seismic zones, and certain modifying factors are included for taking other parameters into account. The response spectrum technique or dynamic analysis of structures is permissible as an alternative. The aim of this paper is to state the various parameters affecting the design seismic acceleration at any point of structure, examine, if such parameters are given any weightage in the present codes and suggest a unified approach to obtain rational seismic coefficients for designing various structures for earthquake motions. Reference will be mainly made to ‘Recommended Lateral Force Requirements and Commentary’ by Seismology Committee of Structural Engineers Association of California 1968(22); ‘Earthquake Resistant Design for Civil Engineering Structures, Earth Structures and Foundations in Japan’ compiled by the Japan Society of Civil Engineers, 1968(); and ‘IS:1893-1970, Indian Standard Criteria for Earthquake Resistant Design of Structures’ by Indian Standards Institution, 1970(17), These will be briefly referred to as SEAOC, JSCE and IS: 1893 Code respectively in the discussions that follow.