The original Traveller rules existed in several variant forms. Most include the three core books: Book 1 - Characters and Combat, Book 2 - Starships, and Book 3 - Worlds and Adventures. Some also include an introductory Book 0 by Loren Wiseman and various adventures.
This edition of the rules is now often called "Classic Traveller".
Notes on This Edition
A reprint in a single 160-page book with cover by Steve Bryant. Also includes a new introduction by Marc Miller, and a short Traveller fiction piece by Martin J. Dougherty.