The identity of the eighteenth-century polemicist who was responsible for the series of letters to the London Public Advertiser, from 21 January 1769 to 21 January 1772 has long been a subject of debate and speculation. These letters were republished in 1772 as the Letters of Junius. The letters themselves remain after more than two hundred years a most startling example of political polemic and invective. The main part of the Junius collection was acquired in 1999; it had once been in the collection of the Mercantile Library Company of Philadelphia. To this collection has been added materials already held by the McGill University Libraries including a copy of the book on Junius (Junius discovered. Boston: Little, Brown; Montreal: H. Ramsay; Toronto: A.H. Armour, 1854.) by the Montreal lawyer Frederick Griffin (1798-1877) and a number of books related to Junius from his library. The collection comprises some 145 editions from 1769 to 1909 mostly in English but including French and German translations, and the two bibliographies by Francesco Cordasco (1974 and 1986). In addition, there are four volumes of manuscript and printed material complied by W. Eames originally in the collection of the Mercantile Library Company. Records for the holdings are in the McGill Library on-line catalogue.