Wales has become the first nation in the UK to introduce a "revolutionary" new system to increase the number of organ donors.
From Tuesday, adults will be regarded as having consented to organ donation unless they have opted out.
More than one million people - 34% of the population - have registered to opt in already and 86,000 have opted out.
Health Minister Mark Drakeford called it a "ground-breaking step which will save lives".
He paid tribute to the cross-party support for the change in the law, which aims to increase the number of donors by 25%.
In the past year, 14 people died whilst waiting for a transplant in Wales, while there are currently 224 people on the waiting list, including eight children.
The so-called soft opt-out system will now apply in these circumstances:
- For people aged 18 and over who have lived in Wales for more than 12 months - and who die in Wales
- A person will become a potential donor either by registering their decision to opt in - as they do currently - or by doing nothing at all, in which case their consent may be deemed
- If families knew their loved one did not wish to be an organ donor - even if they had not opted out - they will still be able to tell doctors and donation will not take place
- More information about the organ donation system
- Organ donation in Wales - Q&A
- Behind the scenes with the transplant team in Cardiff
In the rest of the UK, the opt-in system still applies, although ministers in Scotland and Northern Ireland are likely to be watching what happens in Wales closely.
First Minister Carwyn Jones said it was "law making in Wales at its best".
Ministers have said more than two-thirds of people in Wales are now aware of the changes and they hoped a "leap in consent rates" would follow.
Mr Drakeford said: "There are many, many people who would be prepared to be organ donors but the knowledge of their wishes is not available at the point where this very unusual set of circumstances is significant.
"The law is just one thing we're doing; it will be a profound cultural change.
"NHS Blood and Transplant says we need a revolution in consent - we think our law delivers that - and an evolution in practice, and we're part of that UK-wide evolution that will go well beyond 1 December."
He said he was satisfied the balance was right and people had for the very first time the right to register their decision to opt out too.
But the known views of the donor would prevail.
Mr Drakeford said he welcomed the support of faith groups although there was still some opposition to presumed consent.
The Rt Rev John Davies, Bishop of Swansea and Brecon, said the churches were fully supportive of the issue of organ donation but the preference was to see it as a "gift."
"In the deeming of consent, there is always the risk that that idea of gift might vanish," he said.
"From a Christian or moral perspective, I think the idea of giving someone a precious gift is something much better than others presuming that that gift can be eradicated and just taken."