Eurostar: London to Amsterdam via Brussels-train question?

There are two ways to travel between Brussels and Amsterdam: Thalys high-speed train, or the regular inter-city trains. The Thalys high-speed trains require advance reservations via www.thalys.com, and the discount tickets lock you into a specific departure time; but the journey is faster....almost an hour. With the IC trains all you have to do is show up at the train station on the day of your journey and purchase the tickets at the windows; those tickets are valid for any IC train. No reservation needed or possible. If you book way in advance taking the Thalys isn't any more expensive than the IC train. Check http://www.nshispeed.nl/en
With this site you can book the entire journey from London to Amsterdam.

Either way, trains leave hourly. Two slight corrections: Thalys works sort like an airline, in that buying a ticket also reserves you a specific seat. But except for some very busy travel days, you can usually purchase tickets on the day of travel. The slower option isn't quite the same thing as a regular IC train. I forget the exact name, but it's something like "Cityline" and it's a special joint service run by NMBS (Belgian Rail) and Nederlands Spoorweg (Dutch rail). The key difference is that you don't have to exchange trains between NMBS and NS at the border station at Roosendaal.

Both the NS Highspeed, and Belgian Rail sites label the direct non-thalys Brussels to Amsterdam train as "IC"-intercity; I've never head of cityline. Tickets are typically available at the last minute for Thalys trains but you will be paying the highest fare. Also you mentioned you are traveling in June. Sometime "mid-2011" it's expected that the new Fyra high-speed service between Brussels and Amsterdam will begin service. If this does happen on schedule the regular IC train service will be canceled, and you will have to use either Fyra or Thalys. Both will require advance reservations.

The point is, no matter what the train is called (I don't remember exactly what they call it), that it's a separate service run by both national rail companies and the rolling stock has a different coloring scheme... ie, if your're riding a train that has a big "B" on the side of it, you will have to exchange at Roosendala. But this service, with different markings, continues all the way to Amsterdam. I only mention it because some friends of mine got confused by the difference. I bought them their tickets from Leuven to Amsterdam, and I probably should have explained a little better which trains to take. Instead of just hopping on the train in question (whatever they call it!) at Mechelen, they took a regular Belgian rail IC to Antwerp, then an IR to Roosendaal, before riding some strange combination from there to Amsterdam. What should have been just over a 3 hour trip took about 6. I only mention this minor point so people can avoid that same mistake.

Thank you all for writing and for your advice! Sincerely,
China