The warden of Oz is Leo Glynn (Ernie Hudson), a tough, no-nonsense man.

Cell Block 5 is the experimental unit Emerald City (Em City), run by Tim McManus (Terry Kinney), a divorced man who has bitter childhood memories of growing up in Attica, NY. In Em City, redemption is the goal. McManus wants to rehabilitate offenders, to give them a chance at a new life when they get out. Each inmate (whether a new prisoner or a transfer from the general population, or "gen pop") is given a sponsor to show them the ropes. Em City has a good mix of drug dealers, gangbangers, racists, and lifers. McManus believes inmates & staff should treat each other with respect.

Recently elected, Governor James Devlin (Zeljko Ivanek) came to office on a "No Perks for Prisoners" platform & reinstated the death penalty. He banned smoking and conjugal visits, not very popular with inmates/staff.

Dr. Gloria Nathan (Lauren Velez) runs the prison hospital. She and McManus briefly dated while she was separated from her husband. While treating Ryan O'Reilly, he fell in love with her, and had her husband Preston murdered by Cyril O'Reilly. She prescribed the drugs used in the lethal injections of Keane & L'Italien.

Sister Peter Marie (Rita Moreno) is head of psychiatric evaluation. She's responsible for arranging conjugal/family visits. Sister Pete is a licensed drug counselor & teaches anger management classes. She briefly quit to protest the death penalty.

Father Ray Mukada (B.D. Wong) is 1 of 2 prison chaplains. He hears confession & reads Mass in the cafeteria. He also arranged for Miguel Alvarez to present at the birth & death of his son at Parker Women's Correctional Facility.

Some the correctional officers (called "hacks") are Diane Wittlesey (Edie Falco), Joseph Mineo (Philip Scozzarella), Lenny Burrauno (Skipp Suddeth), Edward Hunt (Murphy Guyer) & Mike Healy (Steve Ryan).