The Vestiarium Scoticum (full title, Vestiarium Scoticum: from the Manuscript formerly in the Library of the Scots College at Douay. With an Introduction and Notes, by John Sobieski Stuart) was first published by William Tait of Edinburgh in a limited edition in 1842. John Telfer Dunbar, in his seminal work History of Highland Dress referred to it as "probably the most controversial costume book ever written."
The book itself purported to be a reproduction, with colour illustrations, of an ancient manuscript on the clan tartans of Scottish families. Shortly after its publication, it was denounced as a forgery and the "Stuart" brothers who brought it forth, and who claimed to be the grandsons of Bonnie Prince Charlie himself, were likewise denounced as imposters. It is indeed generally accepted today that neither the brothers themselves nor the Vestiarium are what they were purported to be.
Nevertheless, the role of the book in the history of Scottish tartans is immense, with many of the designs and patterns contained therein passing into the realm of "official" clan tartans.
More information on the Wikipedia page