From the back of the book:

Dominant for centuries, House Davion has led the Federated Suns to greatness through brilliant and innovative leadership. The Federated Suns have carved a prominent swath through history: the Davions formed a military that rewrote modern warfare; created the New Avalon Institute of Science, giving the Inner Sphere its first technological renaissance in three centuries; and united the military might of the Federated Suns with the economic power of House Steiner, creating the vast star empire known as the Federated Commonwealth. But with such power comes corruption -- and civil war is looming on the horizon.

BattleTech Field Manual: Federated Suns provides profiles on every Federated Suns regiment, including their loyalties, and provides special rules, new equipment and 'Mechs unique to this powerful House.

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This sequel to the earlier House Davion (The Federated Suns) takes the same format as the other BattleTech Field Manuals in that it focuses largely on the military structure of the Federated Suns before introducing a scattering of new equipment, 'Mech variants, an OmniMech, a Warship and some Battle Armour. In this case, the new technology consists of the Rotary Autocannon, new Autocannon ammunition (although some is reprinted from earlier sourcebooks) and Inner Sphere Targetting Computers.

While this sourcebook is out of print, it has been released in an electronic format by the new license holder, Catalyst Game Labs, making it much easier to get hold of than some of the other Field Manuals.