The German physicist and writer Lichtenberg (1742-1799) was well known during the nineteenth century as a humorist, thinker, and psychologist. He was also a favorite author of Freud, who read him beginning in his teens, quoted him frequently, and called him a "remarkable psychologist." Despite this, he has been ignored by psychoanalysts and historians of psychiatry alike, and most of his writing is still unavailable in English. An introduction to Lichtenberg as a psychologist is provided, stressing material dealing with dream analysis, association theory, and drives. Relevant excerpts are translated into English. Lichtenberg is shown to have insisted upon the need for a systematic and rationalistic study of dreams, to have analyzed individual dreams (describing them as dramatized representations of thoughts, associations, and even conflicts from his own waking life), and to have emphasized the functional link between dreams and daydreams. His remarks on drives and commentary on eighteenth-century association theory represent a significant practical application, and thus refinement, of Enlightenment rationalistic psychology. These achievements are assessed in light of Freud's early fascination with him; it is argued that Lichtenberg is an example of the relevance of the historical and cultural background of psychoanalysis to clinical practice.