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The Adeptus Arbites are the watchers of the law. It is given to them to maintain order amongst the higher echelons of Imperial governance. Wherever a planetary governor seeks to abuse his rule, wherever populist unrest seeks to unseat the rightful dominion of the Imperium, wherever thoughts of personal gain at the Emperor’s expense cross the minds of the ruling classes, there you will find the dogged agents of the Lawgivers.
The Adeptus Arbites is not a galactic police force. It has little interest in petty crimes such as theft, murder or tax evasion, for these fall under the responsibility of the local planetary forces. The Adeptus Arbites is there to keep order on a far greater scale, to root out corruption, maintain the Imperial tithe, and to guard against witchery.
From the Adeptus Arbites come the fearsome Arbitrators. Also known as Judges, these men and women are stoic in their duty and unquestionably loyal to the Imperium.
The relationship between the Inquisition and the Adeptus Arbites is often one of the more cordial within the Adeptus Terra. Arbitrators often see working with Inquisitors as a way of further enforcing justice. However, such arrangements have not always worked out so well. It has been known for Judges to turn on the Inquisitors they had been seconded to serve if they believe the Inquisitor to have broken sacrosanct Imperial laws. This means Inquisitors of the more Radical factions must be wary when recruiting members of the Arbites to become their Acolytes.