Most foreign travelers will come to Brussels either by plane or train.

Arriving by plane at Brussels airport

Website : www.brusselsairport.be

Getting from Brussels Airport (BRU) into the city is easy. If want to see all destinations (outside cities at least) in comfort go for a car.

Train
Make sure you have a ticket that includes the Diabolo supplement, that is required for all journeys to/from the airport.
A train to all 3 main Brussels stations (Nord/Noord, Central/Centraal and Midi/Zuid) runs from the airport station located at the -1 level of the terminal. When you get out of the arrival hall, take the lift or escalator on your right to go down, and you’re there.
Tickets can be bought at the counter in the train station hall. In case they are closed, a ticket can be bought from vending machines (they only accept Maestro cards). If boarding a train without a ticket, it can be bought on board, but notify the attendant when getting on the train, to avoid paying a fine.
You can also order tickets online (but if not a Belgian citizen, they must be printed out) at www.nmbs.be

To/from Brussels and other destinations in Belgium :
Journey time into/from Brussels is 20 minutes. and trains start running from the airport at around 5:30 am until past midnight.
From Brussels, the first train is at around 04:40 hrs and the last around 23:00 (from Bruxelles-Midi)
A ticket costs €7.60 in second class.  There are 4 trains per hour to Brussels. If taking the train at the weekend, check the schedule as it might be different.
The safest is Brussels Central station. Brussels North is a very unsafe place after dark. Also Brussels South/Midi is not a very safe neighbourhood at night.
For other destinations, the best option is to take the train to Brussels (Nord, Central or Midi/South) and change there to your final destination (Ghent, Bruges, Liege, Antwerp). Some trains go directly from the airport to seaside.
The Thalys and Eurostar trains leave from / arrive at Brussels South/Midi.

To/from Leuven :
You can also take a train from/to the airport directly to/from Leuven (direct train 2 times an hour, €5.30, 15 min). Some continue to Liege. The trains run in general from 5:00 hrs until 23 hrs. Leuven is also a good transfer station to go to Liege/Luik, Hasselt, Genk, Eupen, Maastricht, Mechelen.

Bus
The bus terminal is located one level above the train station (coming into the arrival hall from the baggage claim area, go to the right and down with the lift/escalators.
There is an airport bus line, line 12 or 21, depending on the day you arrive, between the airport (level 0, follow signs from escalator) and rue de Trèves (stop outside Fabian O'Farrell pub) near the Luxembourg railway station. Buses start from Brussels City from 05:00 and from BRU from 5:40 am; on Saturdays, Sundays, public holidays and weekday evenings, line 12 is replaced by (non-express) line 21 starting and terminating at Ducale (near Trône metro station), which runs until around 23:00 depending on the day; see schedule   Both stop at NATO,  Diamant pre-metro station where you can change onto trams 23, 24 or 25 (to Schaerbeek/Rogier/Heysel in one direction and Montgomery/Ixelles/Uccle in the other); Schuman, where you can change onto the metro for e.g. Arts-Loi, Gare Centrale, St. Catherine; and Luxembourg.
Tickets cost 4€ from a ticket machine (there is one next to the bus stop at BRU), which can be paid using coins (no bills are accepted) or credit card and are valid for any number of changes to/from other STIB buses, trams, metros, within 60 minutes of first stamping (but you have to put the ticket in the orange machine again when changing to another bus/tram or entering metro system).

The most efficient solution depends on your exact destination in Brussels, for example for Eastern communes like Evère and the Woluwes, as well as the European quarter (Schuman-Luxembourg)  it would be the bus whereas if you are headed for the city centre it would be the train. For more information (and alternatives) about going to or leaving the airport, see the website for  Brussels Airport

Taxi / rental car (see other section)
The taxi stand is immediately outside of the airport. Only use taxis from the queue to avoid even worse prices to get anywhere. Most taxi drivers are French-speaking.
Car rental is located in the arrival hall, to the right when exiting the baggage claim area. 

It's almost impossible to walk from the airport to nearby cities.  In Belgium, it is not a habit to flag down cars.

Departing by plane from Brussels airport

There is only 1 checkin area in Brussels Airport, split up into a part for scheduled flights and one for chartered flights.
Flights inside the Schengen area (and recently SN Africa flights and SN flight to JFK) depart from pier A, while non-Schengen flights depart from pier B.
Pier A is quite a long walk from the checkin area (10-15 minutes to the first gate, 15-20 minutes to the last, without counting the time to pass through security), while pier B gates start almost immediately at the checkin area.
While walking in the tunnel to pier A, be sure to look to the left in the middle of the tunnel to see yourself through thermal cameras on the big screens (at time of writing in 2011).
Per pier there is a single security area, so depending on the time of day/period, queues grow fast to about 30 minutes waiting time.
A fast lane is available during the day for business class and privileged members.
There is quite a number of shops after the security area in pier A. (restaurants / clothes / specialities / cosmetics / books / toys / travel).
Pier B has some shops before security, and only a couple after security (Belgian specialities), so be sure to get anything except Belgian specialities before security. Lounges are near the beginning and end (SN Africa flights) of the gates at pier A, and at the beginning of the gates at pier B.
It is wise to get to passport control as fast as possible when getting out of the plane, since the number of booths is limited, and queues can be long.
Sleeping  at the airport is quite hard, since most seats fit only 1or 2 persons (benches with 4 seats with metal separators between the seats).
Pier A gates with a number lower than 30 are for planes with apron positions, so these gates are serviced by buses, while all other gates of pier A and B are jetties.
The airport offers WIFI (Telenet hot spots in 2011), but it isn't free. In the business lounges, vouchers for free access are available at the reception.

Parking
Near the airport, 3 parking buildings are available. P1 is the nearest to the departures/arrivals (10min walk), but also the most expensive (more than 20 euro / day). P2 is slightly better priced, and a good 10-15 minute walk from the main terminal building. P3 is the cheapest and about 10-15 min walk from the terminal building. P3 also offers promotions such as 3 days for the price of 2 (50 euro), 9 for the price of 7(100 euro).

Brussels South airport

The name is very misleading, since the airport is actually located in Charleroi, and nowhere near Brussels.

From Brussels-South/Charleroi (CRL): a big Irish low-cost airline has chosen Charleroi to establish its continental hub and others have followed. Approximately 45 minutes away from Brussels, you have 2 possibilities : either the shuttle bus to/from rue de France next to Bruxelles-Midi station for €13 single, €22 return; or regular public transport, using bus A/68 to Charleroi-Sud station then train to Brussels or any other destination in Belgium. For the latter, a flat-rate "combo" ticket can be purchased from machines at the airport for €19.40 to any Belgian station (see CRL website).
A taxi to Brussels center will cost €90 (fixed prices apply). Taxis from Brussels are more expensive, a trip to the airport will cost €120 when booked in advance, othervise up to €170.

 

Train

International trains such as Thalys, Eurostar or the German ICE stop at Bruxelles-Midi/Brussel Zuid station. It’s quite easy to leave the station using public transport, either the Metro (Line 2 that follows the limits of the "Pentagon", the city of Brussels itself) or the Pre-metro (in fact, an underground portion of the tram system) that crosses the city from North to South (more details on the public transport page). If you have a lot of luggage, a taxi may be the best solution. Look for the taxi signs in the station’s hall. They are just outside the station. Beware that taxis in Belgium are expensive.

 

Boat

It is also possible to arrive in Brussels by boat e.g. www.easyCruise.com cruises in and out of Brussels to a mooring on the Canal du Midi not too far from Gare du Nord. www.tui.com also cruises the river/canal. You can take a trip to Antwerp, Rotterdam and Amsterdam along the river / canal system. Easycruise prices start from GBP9 per cabin per night depending on promotions and how early you book. See Inside Page: Cruising the River