The Ordo Xenos is the arm of the Inquisition that turns its gaze outward, to the countless alien species that hunger at the edges of human space. Its Inquisitors dedicate their lives to understanding the xenos threat in all its variety, from the devouring hive-fleets of the Tyranids to the subtle deceptions of the Aeldari and the patient expansion of upstart empires. To defeat an enemy, the Ordo teaches, one must first comprehend it, and so its agents amass forbidden archives on the biology, culture, and war-craft of Mankind's rivals.
Such study is perilous, for the line between scholar and sympathiser is thin, and more than one Ordo Xenos Inquisitor has been condemned for trafficking in alien artefacts or bargaining with the very species they were sworn to exterminate. Yet knowledge is a weapon, and the Ordo wields it without apology, deploying its insight to guide Imperial crusades and pre-empt invasions before they can gather strength.
When investigation gives way to war, the Ordo Xenos calls upon its Chamber Militant, the black-clad Deathwatch, elite Space Marines seconded from a hundred Chapters to serve as the Imperium's specialist alien-killers. Their exploits and their vigil are chronicled in the account of the Deathwatch, a brotherhood forged expressly to meet the xenos in close battle.
Like all who number among the Inquisition's Imperial Agents, the Inquisitors of the Ordo Xenos operate with sweeping independence, requisitioning what they need and answering only to their conscience and their conclaves. Their doctrine and duties are set out in the glossary entry on the Ordo Xenos, watchmen upon a frontier that stretches without end into the hostile dark.