Travel to Europe

The separate countries will decide.
There is most likely some matrix of #of cases per #population and number of days of sustained reduced new cases.
Also bear in mind countries allowed in hsve varied and 14 day quarantine has ser saeed between requiring it or not. It is far from a stable plan.

The European Union - they would strongly prefer that individual countries don't go their own way, but rather have a consistent set of standards (obviously that's an ideal). They already have a set of conditions published but, no doubt, these will be tailored to meet current needs over time.

That would be the EU, or its member countries. The list of allowed countries is adjusted every 2 weeks and is based on the prevailing COVID infection rates in that country. Here's a link to a previous thread. The EU document is linked in the first post. https://community.ricksteves.com/travel-forum/general-europe/what-eu-s-new-border-recommendations-mean-for-travelers

Thanks Do you have a link to the conditions?

Read the info in the link below:
https://ec.europa.eu/info/live-work-travel-eu/health/coronavirus-response/travel-and-transportation-during-coronavirus-pandemic_en

It is up to each EU member. The EU itself offers guidance but a member country doesn't have to follow it. As of now, most are following the same criteria. (As an example, Hungary closed its border to all foreign visitors earlier this month including those from other EU countries. The EU is trying to fight it but so far has not been successful.)

You can try the website http://www.covidcontrols.co

It is kept pretty much up to date as to rules. You can even set it as to which country you are coming from to get rules tailor made for you.

Cases of Covid-19 are beginning to pick up in many EU countries so the rules can literally change daily.

Nick and Frank II nailed it. Interesting note, for a period of time Hungary was letting in US citizens while excluding some European citizens.... so it can be a mixed bag. A few non-EU countries are currently open to US citizens, but for how long? I think there will always be push back on EU standards as its a ones size fits all approach.

I don't know what the criteria might be to lift the ban, but right now, since Sept 1, the US has had almost twice the new cases per capita as western Europe, so I don't see them lifting the ban soon.

And cases like this, American spreads virus in Germany, certainly won't help.