The Klingon Dictionary
The Klingon Dictionary is the primary source that describes the Klingon language. The first half of the book is a description of the grammar, and the second half contains vocabulary lists, arranged in both English->Klingon and Klingon->English. (One should note that there are some words which appear in one side and not the other.)
The original 1985 edition is a smallish trade paperback, with a Klingon Bird of Prey depicted on a blue cover, and having yellowish pages with gold edging. The cover picture on the earliest printings is embossed; later printings are flat.
A second edition was published in 1992, in a larger format and with a glossy white cover showing a photograph of three Klingons (Christopher Lloyd as Kruge, John Larroquette as Maltz, and Stephen Liska as Torg) from Star Trek III: The Search for Spock. (The same photograph appears on the box of the Conversational Klingon audiotape.) The contents of this edition are page-for-page identical to the first, typographical errors and all, but it also includes an Addendum at the end with a few pages of additional grammatical clarifications and some more vocabulary.
There is no official count available of the number of copies purchased, but in the late 1990's it was said to be more than a quarter of a million.
The chief of the canonical sources.