But onwards plans are relevant because CBP officers evaluate things like intended length of stay / lack of stay, whether you have onwards/return tickets, etc. After all this is declared on the blue form. They might be more lenient if it's clear you're in transit vs trying to visit the US.

Without evidence to the contrary I wouldn't assume that they'll return someone who is inadmissible as opposed to escorting them to the flight they already have tickets for. Your citizenship and residency of third countries might also play a part in this, especially if the onward flight is to your home country.

Finally, doesn't IAH (or possibly MIA) have simpler arrangements for international transit? Still involving CBP but no luggage handling?

The problem is that there is no physical separation of international passengers in US airports.

I think its generally CBPs policy to escort you onto a flight that is either your country of citizenship or a country you have the right to work/live in. On a recent flight I saw an Australian man being escorted onto a plane by CBP to Canada.

I can't see them sending people back to a country they are neither a citizen or work permit holder off, as the person could just get stuck of a loop of being sent backwards and forwards.

A few airports in the US, such as DFW, MIA, and IAH, have a process called ITI where bags on an international-international connection are automatically transferred, so the traveller doesn't have to pick up their bags at the connection. They still have to go through immigration though and go back through security. Note the bags need to be tagged for ITI and not all airlines participate. It's best to ask at check in.

Just curious, if you got stuck in a loop like that....who pays?

The airline has to cover the cost. There have been a couple of reported cases of this happening. I suppose with most countries you can send someone back and they can be put on another flight to their home country as the majority have an international transit area.

If you only sent people onwards to places they had a ticket to there would be no chance of a loop. If the destination rejected them the ticket would be used, no more loop.

Just to add some small note here

There is a international transit , from certain locations (I assume not all) and certain airports what happens is this

your bags are tagged international-international transfer, you do NOT pick them up in the US , next time you see them it will be at your final destination

you also can go through a special transfer desk, where you do NOT get your passport stamped (this I thought it was odd, but thats what happened)

you then rejoin the normal reclear security line etc

this exists in IAH,DFW (and I think also EWR but dont recall) , MIA also must have it

Is this desk similar to transfer desk at PVG (where you basically bypass going in front of immigration officer)? Or is it just different procedure?

Bcos, I transited at recently (intl to intl) and had to clear immigration.

That expedited procedure is also discussed in this thread:

Wolfie, I hate to say it, but you're wrong. I don't care which US airport you transit at, you have to go through US Immigration and Customs. There's no way around it.

You are all wrong and should do a bit more research before making incorrect global pronouncements. Particularly, it is galling to have others repeat incorrect information after the correct information has been posted:

and

It is extremely confusing to equate Immigration and Customs, even though both are administered by Customs & Border Patrol (CBP). Indeed CBP runs an International-to-International (I-T-I) program at DFW, MIA, and IAH for checked luggage which is specially marked with an ITI tag.

This has nothing to do with Immigration or with Customs for carry-on luggage. The bottom line is that there is no such thing as "transit" in the US and has not been since the 1990's. There are some limited physical arrangements such as the NZ arrangement with CBP at LAX, but that is not relevant to this thread and deals only with a unique physical gate situation. It is simply a decision by CBP not to inspect passengers who remain penned in a specific gate.

If you are deemed inadmissible to the US, you would either be returned to the country from which your flight originated, your country of citizenship or residence, or a country which the US is assured will accept you. If your inadmissibility is due to the failure of documents, the financial responsibility for your return befalls the carrier that brought you to the US. If you are properly documented but otherwise deemed inadmissible, the financial responsibility befalls the US.

I know of at least two people who have been deemed inadmissible, but who have been permitted to continue their onward journey after the onward destination country advised CBP that they would be admitted on arrival. CBP gave them the choice to be returned to their origin or to be escorted to their onward gate. They gladly chose the latter and were discretely escorted by an Officer to their departure gate.

Your bags might not have to go through Customs. You, however, do. Immigration, then Customs. The fact that you only have your carry-on baggage and whatever is in your pockets is irrelevant.

This sounds too sensible to be true.

I recall a thread from a couple of years ago where someone claiming to be a CBP officer said the pax would always be sent back to their originating point.

So, if you know you are inadmissible to the US but somehow have a valid ESTA, you can still transit the US (provided that you are more or less guaranteed entry to your destination)?