The Imperial Security Bureau is the "security division" of The Galactic Empire. Its agents take overt action to encourage both the populace and military personnel alike to remain obedient to Imperial policy and ideals.
Before the Battle of Endor, the ISB was an important branch of the COMPNOR political party. (COMmission for the Preservation of the New ORder.) This political organisation has long since dissolved, but the ISB remains intact, in service to the Empire. As has always been the case, it is composed of security officers who police the Empire, strive to maintain moral, and uphold Imperial ideals.
They accomplish this via ensuring that the Galactic Empire's Imperial Law is upheld. They will deal swiftly with any violators, as these documents aim to satisfy the interests of the Empire, and its officers, as a whole. Outside of regular investigations, ISB personnel are often employed in various engagements for the overall betterment of the fleet...
As a security officer, you are part of a force which strives to maintain the Empire internally, while others fight externally on its behalf. ISB officers are loyal to the Empire above all, for its agents maintain the integrity of Imperial Law on a day to day basis...!
Beyond what is visible here, the operations of the Imperial Security Bureau are, naturally, classified, and not available for general browsing. Further information is strictly on a "need-to-know" basis. You will be provided with further clearance as your rank, position, and clearance allow.