This article presents what is possibly the first English translation of a 1930 manuscript related to Vygotsky's work (probably written by Vygotsky himself). This manuscript, the Zalkind Summary, is a five-point summary of his presentation to the First All-Union Congress on the Study of Human Behaviour in Leningrad in January 1930. This article provides an account of the circumstances leading to the Zalkind Summary's discovery and explores several aspects of it in relation to contemporary appreciations of Vygotsky's psychology, most notably the functional method of double stimulation and the precise experimental data used by Vygotsky to document key theoretical constructs in concept formation processes. The method of double stimulation for the study of concept formation, as developed by Sakharov under Vygotsky's leadership and handed down to scholars in the West by Hanfmann and Kasanin, is compared to the works of various scholars, past and present. This article concludes that the Zalkind Summary is more than a footnote to history: It is a stand-alone theoretical and empirical statement of central and intriguing import to Vygotskian psychology. (Contains 5 figures, 1 table, and 7 footnotes.)