Classification of the history of science has a long history, and the essays in this Focus section explore that history and its consequences from several different angles. Two of the papers deal with how classifying schemes in bibliography have evolved. A third looks at the way archival organization has changed over the years. Finally, the last essay explores the intersection of human and machine classifying systems. All four contributions look closely at the ramifications of the digital revolution for the way (...) we organize the knowledge of the discipline. (shrink)