BattleTech boxed sets have been including a booklet separate from the core rulebook since 1996 that fans colloquially refer to as "Universe Book". Current publisher Catalyst Game Labs refers to the booklet, which is also downloadable from their website, as the BattleTech Universe Guide although the word "Guide" never appeared in any of the titles the booklet ever had.
The booklet serves as an introduction to the BattleTech universe, portraying the setting's history, the Great Houses and other factions, and the roles of BattleMechs and MechWarriors within the setting. Title and exact content have repeatedly changed over time as new editions of the boxed set were published; consequently, there are a number of different booklets and editions thereof that can be referred to as "(the) Universe Book".
Universe Guide books
Introduction to BattleTech
Introduction to BattleTech, the precursor to what would evolve into the later Universe Books, was first included by FASA with the BattleTech, 4th Edition boxed set that came out in 1996. Although this was the first time that another booklet was included with the boxed set besides the rulebook and the record sheets, it was not a pure setting book as it also contained the Quick Start Rules.
Classic BattleTech Universe
After 2001, the original BattleTech game line was rebranded to "Classic BattleTech" and the rights were transferred to Wizkids who licensed them to FanPro. FanPro published a new edition of the boxed set in 2003 that included a booklet titled Classic BattleTech Universe. Focused on introducing the universe, this booklet expanded on the setting information from the previous booklet and included an introductory short story. It would become the template for subsequent Universe Books for a long time to come.
FanPro made a digital version (PDF) of the booklet available for free download via their website, classicbattletech.com (now defunct). It had a slightly different cover, with the BattleTech logo graphics updated to the latest logo. After the BattleTech license went from FanPro to Catalyst Game Labs, CGL also made it available for free download, though the logo on the cover was changed again when "Classic BattleTech" reverted to simply "BattleTech".
Inner Sphere at a Glance
Having taken over the BattleTech IP from FanPro, CGL published a new edition of the boxed set in 2007 for which they retitled the print edition of the booklet to Inner Sphere at a Glance. It was otherwise essentially unchanged from the previous booklet, with some extra content.
Inner Sphere at a Glance was republished with the 2011 and 2013 editions of the boxed set, with only minor changes such as adjusting the logo on the title to read "BattleTech" instead of "Classic BattleTech", swapping the short story out for another fiction piece, adding some information about the Clans and their technology, and adding entries to the Technical Readout section in accordance with the contents of the respective boxed set.
The 2019 boxed set, BattleTech: A Game of Armored Combat, came with a completely redesigned and much shortened 16-page booklet titled BattleTech Primer.
(Meanwhile, the downscaled BattleTech: Beginner Box that was published simultaneously with A Game of Armored Combat only contained a flyer-style folded map of the Inner Sphere titled An Instant Guide to the Inner Sphere. Focused on the year 3025, it offers some bullet points about the five Great Houses and Comstar, the Inner Sphere and the BattleTech universe at large, BattleMechs, and MechWarriors.)
Notably, there is a digital version of the BattleTech Primer (in PDF) with the same cover but featuring vastly more content, with three times the pagecount of the physical booklet in the box. CGL used to have it as a free download via their BattleTech website, but the current website does not have a download link anymore.
- Download link for the (Classic) BattleTech Universe booklet from the BattleTech.com website as provided by CGL