From the back of the book:
"Not every interstellar power can afford the likes of the Wolf's Dragoons. Not every world has the resources to hire even a lance from the elite Kell Hounds. That doesn't mean war doesn't come in the form of objective raids, internal power struggles or outright piracy to such factions and backwater worlds. For such, any mercenary group will do, even the dregs. If they can point and shoot, someone, somewhere, will hire them.
A companion volume to Classic BattleTech Field Manual: Mercenaries, Revised, the Mercenaries Supplemental provides an in-depth look at a few of the best and many of the worst known Inner Sphere mercenary commands, including histories, officers, and favorite tactics. Special rules allow players to use these commands in their Classic BattleTech campaigns, while a new point-based construction system provides an optional way to generate mercenary commands."