Thalys is a high-speed train network built around a dedicated track between Paris and Brussels. This track is actually shared with Eurostar trains that go from Paris or Brussels to London via Lille and the Channel tunnel. The trains are TGVs (train à grande vitesse), with modifications that enable them to run on several different types of power supply.
Beyond Brussels, the main cities Thalys trains reach are Antwerp, The Hague, Rotterdam, Amsterdam, Liège, Aachen and Cologne. Trains to these destinations run partly on dedicated high-speed tracks (some of these are yet to be built), and partly on older tracks shared with normal-speed trains.
From Paris, the French high-speed network has high-speed links to other French cities including Avignon and Marseille, Geneva in Switzerland, and also Paris's main international airport Charles de Gaulle (Roissy) and the Disneyland theme park in Marne-la-Vallée.
The link with the Charles de Gaulle airport allowed Air France to cancel its air service between Paris and Brussels; instead, Air France books seats on Thalys trains.
Thalys as been given the IATA designator 2H. This is used in conjunction with American Airlines and Northwest Airlines. American Airlines has a codesharing agreement with Thalys for rail service from Charles De Gaulle airport to Brussels's Midi. Northwest has a codesharing agreement with Thalys for rail service from Schipol airport Amsterdam to Antwerp's Berchem Station and Brussels Midi.