The Foster and Wolfson polarization paper is widely known and cited, and is fundamental in the literature on bipolarization and the disappearing middle class. The paper has, however, existed only as a mimeo, since 1992; somehow, it never got published (more on that later); we are proud to publish it in full here, at last, in our series of "Rediscovered Classics" in the Journal of Economic Inequality. We thank James and Michael for allowing this.As many readers will already know, this paper develops the 'polarization curve'-characterized by Michael in Wolfson [17], page 406, as playing "the same 'gold standard' role for the concept of polarization as the Lorenz curve plays for inequality". This curve indicates how far each population percentile's income is from the median income; inter alia, the middle class is unambiguously smaller (viz. the distribution is more spread out from the middle) if and only if its polarization curve is everywhere higher. The paper also proposes a Gini-like index measure of bipolarization based on the curve. These constructions have become central in the study of bimodality (or polarization or, as James likes to call it, bipolarity), as is evidenced, for example, by the fact that the Distributive Analysis Stata Package (DASP) of Araar and Duclos [2], in its version 2.0, has modules for estimating and comparing Foster and Wolfson bipolarization measures.James and Michael began the planning for this paper in December 1989, after Tony Atkinson suggested that they should collaborate to probe more deeply the question of measuring polarization-a question that had interested Michael since the days of Love and Wolfson [13], where the concept of increasing bimodality was introduced into the study of income inequality in order to focus on the issue of a disappearing middle class.