From the back cover:
For two centuries, the Clans have genetically bred their warriors. Clansmen are evaluated from birth, with their entire lives revolving around Trials of might-makes-right that whittle away the chaff and create the ultimate soldiers. Dive into this unique warrior culture and battle your way to glory to gain a Bloodname and pass your superior genetic legacy to the next generation.
The MechWarrior's Guide to the Clans is the second volume in the MechWarrior's Guide series for MechWarrior, Third Edition. It provides you with all the material you need to launch your own Clan campaigns. This volume contains seventeen new affiliations, as well as more than a dozen new Life Paths unique to each Clan, complete information for campaigning among the Clans and a full-length adventure.