They each assist the Archbishop of Sydney by maintaining delegated episcopal oversight over a particular geographical area.
Prior to the formation of the current "regions" arrangement in around 1967, the archbishop was assisted by a number of suffragan bishops with no particular geographical area (nor expectation to succeed to the diocesan see).
Effective from 1 July 2021, the regions were changed to plan for Sydney's future growth in the southwestern areas.
The Northern Region covers from Port Jackson to the Hawkesbury River and from the Hills District to Palm Beach.
The South Western Region covers the south-western areas of Sydney stretching from Campsie to Campbelltown and including Liverpool, Bankstown and Fairfield.