The Government of Wales Bill proposes the biggest transfer of power from Westminster to Wales since the Welsh Assembly was set up in 1999.
Once it becomes an act, the legislation will give powers to the assembly to make laws in Cardiff Bay.
But - and here's the crucial bit - each time the assembly wants to change the law it will be dependent on votes in both Houses of Parliament to obtain permission to get on and make those laws.
Q: What will the assembly be able to do that it can't do at the moment?
At the moment the assembly often faces frustration in waiting for parliament to find the time to make laws for Wales.
Let's take a current example. The assembly government is to set up an older people's commissioner - a champion for pensioners' rights.
The bill to establish the role is about to complete its passage through parliament after waiting in a queue.
Under the new, streamlined, system, the assembly will seek approval from Westminster to draft the legislation itself - and then get on with the job.
Q: But the assembly still won't be able to do everything it wants to?
No. It'll only be able to make laws - or "assembly measures" as they'll be known in areas for which it already has responsibility eg health, education and tourism. For example, it couldn't create a bank holiday on St David's Day or legalise fox-hunting.
Those issues will still be decided at Westminster, although some ingenious AMs may test the new system's ability to challenge these issues.
Q: How would the new system work?
The assembly first minister will ask the Welsh secretary for permission to legislate in a particular area. If he says yes, and both Houses of Parliament in Westminster agree, the major legislative work and scrutiny would then be transferred from London to Cardiff Bay
Q: Could the assembly get full law-making powers like the Scottish Parliament?
Yes. The Government of Wales Bill does allow the assembly to hold a referendum on this, if two thirds of AMs want one. In practice, that means Labour has a veto on the referendum option. Should, for example, a Conservative Government at Westminster be hostile to a Labour-controlled assembly, then this route to full law-making powers might be taken.
Q: Does it change Rhodri Morgan's status?
Mr Morgan has long styled himself first minister of the Welsh Assembly Government, even though he is legally only the first secretary of the national assembly's executive committee. The Bill will give him his preferred status and formally separate the assembly government, the executive, from the assembly as a whole.
Q: The UK Government plans to use the act to change the electoral system. Why?
In the last assembly election in Clwyd West three of the four defeated candidates made it into the assembly. They got it through the back door, under the highly-complicated regional list system of proportional representation.
The UK Government says that's unfair and confusing. Welsh Secretary Peter Hain claims it makes winners out of losers. So the act would force would-be AMs to choose one or other route next time.
Opposition parties say this is rigging the system because as things stand it won't damage Labour as much as other parties. The government watchdog the Electoral Commission has also criticised the change.
Q: Will the UK Government get its way?
Giving further powers to the assembly has been the most divisive issue in Welsh Labour politics, but the compromise on offer has pacified sceptical MPs. Labour doesn't have a majority in the House of Lords so ministers expect a tough battle on their plans to change the electoral system.
Q: What happens next?
The Bill is due to become law on Tuesday when it gets Royal Assent. The assembly will then assume its new powers after the elections in May 2007.
Q: And the Queen gets a bigger role in Welsh life...?
Yes. If you look at the small print today you'll find that the first minister will in future be appointed by Her Majesty on the nomination of the assembly, rather like the prime minister or Scotland's first minister.