Karl Ludwig Kahlbaum (1828-1899) spent most of his professional career as director of a private psychiatric sanatorium in Germany. He remains influential for introducing his "clinical method" (based on considering the course of an illness as well as the signs and symptoms) of differential diagnosis of specific psychiatric syndromes and urging abandonment of the more unitary views of psychotic disorders favored by the leading German academic theorists of his time. Kahlbaum's approach to nosology, detailed in an 1863 monograph and other works, strongly influenced Kraepelin's views. However, remarkably few of the important writings of this keen clinical observer are available in English translation. His seminal lecture-essay "On Cyclic Insanity" [Uber cyklisches Irresein] of 1882 is translated into English here for the first time, with comments about its place in the history of the evolution of the concept of bipolar disorder, including its position as a link between Falret's folie circulaire and Kraepelin's manic-depressive insanity.