- For a list of mercenary units, see Category:Mercenary Commands
In the Inner Sphere, private, contracted military units have been doing a lot of the fighting. Some are only in it for the cash, some for principle, but, whatever the reason, mercenary forces run the gamut from some the most disreputable to some the most elite troops around. Many mercenary companies do not survive their first battle, but dozens have gone on to become successful, trusted units that form key parts of their employers' defenses.
Following the demise of the Star League, warlords and private armies sprung up in vast numbers to fill the power vacuum. They have a place in the quasi-feudal political structure of the great Houses, and remain an important aspect to this day. Their size and composition range from the proverbial lone infantryman hiring his services all the way up to full combined arms regiments complete with DropShips, JumpShips and support units.
 The mercenary business
ComStar originally used to regulate mercenary contracts through their Mercenary Review Board (MRB), which was replaced by the Mercenary Review and Bonding Commission (MRBC, jointly administered by ComStar, all great Houses and mercenary representatives) in 3052. Registration with and regulation through the the MRB (later MRBC) is mandatory for a given mercenary unit in order to be considered legitimate, otherwise it is usually regarded as a bandit force. This gives the MRB/MRBC and their rating system an uncontested monopoly over establishing a given unit's reputation, and the power to arbitrate alledged breaches of contract and even declare a unit rogue.
The longtime overall center of the mercenary business used to be Galatea, then known as Mercenary's Star. It was gradually eclipsed in this role by Outreach after 3030 until the latter was devastated in the Jihad. At any given time, a number of various other worlds feature notable Hiring Halls for mercenaries as well, some more reputable than others.
Quite a few among the vast number of mercenaries stand out, owing to their special history, outlook or connections. The Eridani Light Horse, for example, is one of those that take pride in being a remnant from the SLDF. Others, like Wolf's Dragoons or Snord's Irregulars, have their own agenda besides their mercenary business. Some units such as the Kell Hounds are not truly independent, but are affiliated with one particular House or faction; others are tied to a specific landhold or planet, like the Northwind Highlanders.
Some mercenary forces are mutinous regular forces who abandoned their original masters; examples include the 21st Centauri Lanciers and Hansen's Roughriders. Conversely, others are tied to a single employer through long-time contracts, and occasionally become regular forces of that employer, like McCarron's Armored Cavalry and Team Banzai.
The distinction between regular armed forces, mercenaries, private security forces, privateers and outright pirates is often blurred. A mercenary unit can be classed as "rogue" by the MRB/MRBC breach of contract or war crimes. Others descend into piracy for need of spare parts or while fleeing from obliteration. (The Company Store, a deliberate effort by employers to bring mercenaries near bankruptcy to gain absolute control over them, is a frequent cause for discord and may force units to either renege on their contracts or face absorption by their employer.) Conversely, the pirate forces of the Oberon Confederation were occasionally hired out as mercenary troops, as are in fact most pirate bands.
Arguably the most famous mercenary units are Wolf's Dragoons, the Eridani Light Horse, the Gray Death Legion and the Kell Hounds, all of which have a near-mythical reputation and can demand virtually any price they wish for their services.