The Corps is Mother, the Corps is Father.
-- Psi Corps motto
The stated purpose of the Psi Corps is to protect the privacy of Earth Alliance citizens by insuring that telepaths do not use their abilities in an inappropriate manner upon ordinary citizens. To accomplish its mission, the Corps requires that all psionic humans -- typically telepaths -- in the Earth Alliance either join the Psi Corps, go to internment camps, or take drugs designed to suppress their psionic abilities. The Psi Corps has telepathic "hounds" trained to help them locate rogue telepaths, known as "blips" to Psi Corps operatives.
Psi Corps rates all telepaths -- whether they were captured or joined voluntarily -- on a "P" scale that runs from 1 to 12, twelve being the high end. Ranks and roles in the Corps depend largely on a subject's ranking on this scale. Cooperative telepaths with a rating of P12 are automatically trained as Psi Cops, who have the role of policing other telepaths. Virtually all major governing roles within the Corps are held by Psi Cops.
As it is run entirely by high-level telepaths, the Psi Corps' original goal of protecting "mundanes" from telepathic intrusion has long since changed to protecting telepaths from "mundane" threats, controlling all telepaths for their own ends, and manipulating "mundane" agencies to improve the Corps' own political power. To this end, the Psi Corps arranges marriages for its members with the goal of breeding stronger telepaths.