Definition
The airport, seaport or land border where you first pass through immigration in a country. For Schengen trips, it is usually your first Schengen airport; for Bhutan, Paro or Phuentsholing. Some visas and permits restrict which ports you may use.
Why the port of entry matters
The immigration officer at your port of entry makes the final decision on letting you in, whatever your visa says. In the US, the officer also decides how long you may stay, recorded electronically on your I-94.
Schengen: immigration at the first stop
If you fly Delhi–Frankfurt–Rome, you clear Schengen immigration in Frankfurt, not Rome. Keep your hotel bookings, return ticket and insurance handy there. The Frankfurt–Rome flight is then treated like a domestic one. This is also where the Entry/Exit System registers you.
US preclearance in Abu Dhabi
On some US-bound flights via Abu Dhabi, travellers clear US immigration and customs at Abu Dhabi airport before boarding, and land in the US as domestic arrivals. If entry is refused, you are still in Abu Dhabi rather than stuck in the US.
Land borders
For Bhutan by road, Indian travellers enter at Phuentsholing, where the entry permit is issued. For Nepal, common crossings include Sunauli and Raxaul. Indians need a passport or voter ID at these borders, and permits may be valid only for certain areas.
Example
A Mumbai family with a France-issued Schengen visa flies to Milan via Dubai. Their port of entry is Milan, so they clear immigration in Italy even though France issued the visa. They should be ready to explain why: four of their seven nights are in France.
Practical advice
Keep printouts of hotel bookings and return tickets in your hand luggage, not your checked bag, because that is what officers ask for. See also immigration, and for complex routes, our visa hub.