This paper presents and discusses a number of important topics which affect the determination of seismic design forces in a loading code. These range broadly from seismic hazard through to design philosophy and include the following aspects: influence of uncertainty in determining seismic hazard, seismic hazard parameters, site effects, probability level of design ground motions, role of deformations in seismic design, performance expectations and level of protection. The discussion makes frequent reference to the seismic provisions of both the National Building Code of Canada (1995) and the New Zealand Loading Standard (1992). Also, comparisons are made of seismic hazard and seismic design forces for several Canadian and New Zealand cities.