Covid rules for travelling to the UK will be relaxed for thousands of delegates attending the UN COP26 climate summit in Glasgow in November.
Up to 25,000 government representatives, media and campaigners from around the world are expected.
They will not be required to be fully vaccinated but officials said it would be strongly encouraged.
Vaccines have been offered to registered delegates unable to get a jab by other means.
Under the regulations specifically for COP26, delegates from red list countries will only have to quarantine in hotels for five days if they have been fully vaccinated.
Those who have not received their jabs will have to isolate for 10 days.
There will be no requirement for COP26 attendees coming from amber or green list countries to isolate on arrival to the UK whether vaccinated or not, officials said.
Most people are expected to travel to the conference via London.
Under current rules, people cannot travel to England from red list countries unless they are British or Irish citizens or have the right to live in the UK, with the same rules applying to Scotland with some other limited exceptions.
Those who do arrive from red list countries have to quarantine for 10 days in quarantine hotels, even if they are double jabbed.
There are also requirements to self isolate for 10 days for those coming from amber countries who are not fully vaccinated via approved programmes in the UK, US or Europe.
The red list can change but it currently includes dozens of countries, all of whom are expected to send delegates to COP26, and some of which are among the most vulnerable to climate change.
A UK government spokesperson said COP26 was a necessary event, as the science was clear for the need to take immediate and far-reaching action to have any chance of avoiding the devastating impacts of rising temperatures.
They added: "We know that achieving the ambitious global action needed to tackle climate change requires everyone sitting around the same table. To achieve this, we have been working tirelessly to make arrangements for an in-person event.
"Hosting it safely is of the utmost importance to the UK. Like many recent international events, COP26 will have to adapt in line with Covid."
The spokesperson said details of how the summit would run were progressing after close collaboration with all partners, including public health officials in Scotland and England, the Scottish government, Glasgow City Council and the UN's climate body, the UNFCCC.
"We believe these arrangements strike a balance between allowing critical climate talks at this exceptional event to continue with representation from around the globe, while continuing to have measures in place to protect public health," they said.
Delegates will also be subject to a strict testing regime and they will have to sign a charter agreeing to abide by the protocols for the summit.
The UK is recognising all Covid-19 vaccinations as valid for the event, but officials also said they would not prevent people attending who had not been vaccinated.
The issue of who pays for the regime, including testing and quarantine hotels, has yet to be finalised. Isolation protocols during the event for those who test positive for the virus are also being finalised.
The rules have been signed off by the UK and Scottish governments, but Covid-19 protection measures for the summit could still change, officials said.
A Scottish Government spokesperson said: "COP26 represents the world's best chance - and possibly one of our last chances - to limit global warming to 1.5 degrees.
"The circumstances make this a unique event and exceptional arrangements will be needed to ensure it can be delivered safely and successfully.
"Following close discussions with the UK government and other delivery partners, we are pleased to have agreed measures that will support the full and active participation of international delegates and protect public health."