Do the paperwork before the gate
Vietnam issues e-visas to citizens of all countries, with single-entry and multiple-entry versions available. US passport holders need a visa for a normal visit. The official application portal is evisa.gov.vn.
Type that address yourself. Private sites use lookalike names and sell the same application with a markup, which is an impressive way to pay extra for finding the wrong website.
Vietnam also asks foreign arrivals to fill in a free pre-arrival declaration at prearrival.immigration.gov.vn. The form generates a QR code for immigration and does not replace the visa. Each traveler needs a separate declaration, including children.
I would file the declaration before the travel day and save the QR code offline. Paperwork is much easier while your passport is on a desk than while your carry-on is trying to escape from under an airport chair.
So do the visa check and declaration before leaving home, and use the government domains rather than an ad that happened to buy the top search position.
T2 and T1 are separate buildings
International flights use T2 at Noi Bai. Domestic flights use T1. The buildings sit separately, with a free shuttle bus linking them.
That sounds simple until an international arrival feeds a domestic departure on a separate ticket. You clear the arrival formalities, collect the bag, leave T2, move to T1, and check in again. The terminal change is landside work, not a stroll through a shared gate area.
When an airline sells the whole itinerary together, the connection belongs to the airline. Separate tickets move that risk onto you. If the inbound flight runs late, the domestic booking does not become sympathetic because both reservations contain your name.
I would not hang a tight domestic connection on separate tickets here. Leave a generous gap, or buy the itinerary together and let the airline own the connection problem.
The Red River is part of the airport transfer
Noi Bai lies on the far side of the Red River from central Hanoi. Travelers coming into the city usually cross Nhat Tan Bridge, also called the Vietnam–Japan Friendship Bridge. At night, the cable-stayed bridge is lit across the river. It is a useful reminder that the airport transfer is a real piece of the trip, not the final line of the boarding pass.
The airport express bus serves the terminals, stops near the Old Quarter, and continues to Hanoi Railway Station. That works well if your hotel or next train fits the route. If it does not, forcing the bus into the plan just creates another transfer with luggage.
The Old Quarter and Hoan Kiem Lake sit on the city side of the Red River. If that is where you are staying, the airport bus can get you into the right part of Hanoi, but “near” is not the same as “outside the hotel.” Check the final walk on a map before deciding the bus solves the whole transfer.
Taxis wait outside the terminals. Grab and Xanh SM also operate in Hanoi, so a ride-hailing app gives you another door-to-door option when the bus leaves you on the wrong side of your hotel.
I would choose this transfer from the hotel address: find the actual address, see whether the airport bus leaves you somewhere useful, then switch to a taxi or app if it does not. “Airport bus” is a transport mode, not a personality test.
Hanoi weather changes the buffer you need
Autumn brings cooler air and lower humidity to Hanoi, which makes it the pleasant stretch for walking. Winter turns cool, damp, and often overcast, with drizzle that makes a light layer worth packing.
Summer is hot and humid, with frequent rain and thunderstorms. Tropical storms can also reach northern Vietnam in late summer and early autumn, disrupting flights and trains even when your original itinerary looked perfectly tidy.
This is where I stop treating a connection as a geometry problem. A short gap between a flight and a connecting train may look efficient on a calm screen at home; weather can make that precision useless.
During the wetter part of the year, keep the start of the trip flexible and check with the airline before heading out. Do not make the next leg depend on Hanoi behaving like a spreadsheet.
Going farther: choose rail or another flight before arrival
Hanoi Railway Station is the city end of another useful chain. The North–South Railway runs from there south to Ho Chi Minh City, and its through trains are known as the Reunification Express.
Southbound trains serve Hue and Da Nang, and the coastal stretch between them climbs over the Hai Van Pass above Lang Co Bay. If that is where your trip is going, the railway turns Hanoi into a useful starting point rather than another airport connection.
Vietnam Railways sells tickets through dsvn.vn, which has an English interface, and the e-ticket carries a QR code. Sleeper cabins are available for overnight travel. I would buy through the railway site rather than pay a reseller to stand electronically between me and the same seat.
If rail does not fit the route, domestic flights leave from T1 at Noi Bai, and the terminal question from the start of this piece comes back.
Decide the next mode before buying the Hanoi flight. If the trip continues by train, get yourself into the city and aim at Hanoi Railway Station. If it continues by air, build the terminal change into the connection. The cheap flight is useful when the rest of the chain still makes sense.
