To the reader who is only casually familiar with electrochemical measurements based on periodic perturbations, perhaps one of the most surprising aspects of this review is its illustration of the level and scope of influence of the methodology considered. Hopefully, it has been made evident that the literature gives witness to notable growth in the three areas of importance to any experimental method:theory, instrumentation, and application. One finds successful application to chemical systems whose types encompass the entire range of solution chemistry, from the molecule of life (DNA) to the simplest elemental ions. Having never bothered to actually keep a quantitative record of the output, even this writer was rather surprised upon first realizing that a yield in the neighborhood of 100 publications per year has characterized this field in the last 3½ years. Even in the present era of the "information explosion" this must be considered a nontrivial level of activity. Because many scientists, even among electrochemists, view ac polarography and related techniques as a special peripheral area, it was considered worthwhile to attempt to convey in this review the point that such an outlook is inconsistent with the level and scope of activity one finds in the literature. Consequently, a subject-oriented review was attempted, rather than one oriented toward specific outstanding papers. The latter would have been the easier choice as a shorter, more conveniently organized review could have been generated. Hopefully, the disadvantages with the approach adopted are offset by the fact that this review makes the reader aware of the role being played by the ac polarographic method in widely diversified areas of scientific endeavor. Even more important, it is hoped that an appreciation for the future potentialities of the method and its possible evolutionary pathways has been generated.