Planning permits, building permits, the NCC and what you can and cannot do without approval.
The permit system is where owner-builders and first-time renovators get caught out, because the rules differ by state, by council, and sometimes by overlay on an individual title. Work done without the right approval is expensive to rectify and can stall a future sale.
These guides explain the difference between planning and building approval, when each is triggered, who issues them, and what genuinely falls under exempt development.