The short answer
Restumping and reblocking: replacing the stumps under a house with a timber subfloor. Identical job — "reblocking" is simply what Melbourne calls it. Underpinning: strengthening or re-supporting the concrete footings of a slab or full-brick house. Different structure, different method, different pricing.
Restumping = reblocking
Early Victorian houses stood on red-gum blocks, so replacing them became "reblocking", and the word stuck in Melbourne long after blocks became stumps. Everywhere else in Australia the same work is restumping. Same contractors, same method, same $500–$700 per stump — if you're comparing a "reblocking" quote against a "restumping" quote, you're comparing like with like. More on reblocking.
How underpinning differs
A slab home has no stumps to replace — its weight bears through concrete footings directly onto soil. When that soil fails, you can't swap a post; you have to give the footing new support: dig and pour new concrete beneath it, drive piles to deeper stable ground, or inject engineered resin to re-compact the soil. That's underpinning, priced per metre or per pile, and typically involving a structural engineer from the start. The underpinning pillar covers it fully.
Which does your house need?
Go by what the house sits on, not by which word you've heard. Crawl space under timber floors, ventilation grilles at the base of the walls, a few steps up to the door: stumps → restumping. Concrete floor at ground level, solid underfoot everywhere: slab → underpinning. Older homes sometimes have both — a stumped original house with a slab extension — and can genuinely need both trades; movement at the join between old and new sections is the classic sign.
Why the word changes by state
Melbourne says reblocking; the rest of the country says restumping; Sydney and Adelaide say underpinning more often simply because their housing stock is more slab and double brick, where underpinning genuinely is the relevant job. Queensland adds a fourth phrase — "raise and restump" — because lifting a Queenslander higher while replacing its stumps is routine there. None of these are marketing inventions; they're regional dialects for the same small family of structural repairs.
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Common questions
A contractor quoted me 'underpinning' for my weatherboard house — is that wrong?
Possibly just loose language, but check what's actually specified. A stumped weatherboard should be quoted stumps and jacking, not metres of concrete. If the quote genuinely describes footing underpinning for a house on stumps, get a second opinion.
Is one more expensive than the other?
They're priced differently: restumping per stump (full houses typically $15,000–$30,000), underpinning per metre or pile ($10,000–$40,000 for most jobs). See the restumping and underpinning cost guides.
Do the same companies do both?
Many do, especially in Victoria — the jacking and levelling skills overlap. But underpinning design leans harder on engineering, so check the firm's underpinning work is engineer-designed, not improvised.