This paper is the result of discussions of the study group on Dynamic Analysis established by the New Zealand National Society for Earthquake Engineering and whose brief was to provide some guidance to design engineers on the usage of the dynamic analysis methods that are becoming more common in structural design with the stricter requirements of the seismic loadings requirements of NZS 4203:1992. The paper first of all discusses the concepts of dynamic analyses of single mass systems and then extends this to the modal analysis methods for the analyses of multi-mass systems. The paper then covers a variety of aspects that may be of concern in performing the dynamic analyses and in the modelling of structures.