train from Brussels to Paris

There will be tickets available for the train - they rarely sell out - but you can save significant amounts of money by booking in advance. However, the advance tickets are strictly limited to a single train and you'll have to pay full fare if you are too late for it.

(I didn't think that there were any direct trains from Brussels Airport to Paris. Are there now?)

You can absolutely save alot of money by purchasing tickets in advance. One strategy is to choose a departure time that allows for a late airline arrival into Brussels. This may mean a several-hour wait for your train departure time, but this also allows for a leisurely breakfast/lunch, or even time for sight-seeing. Upon (air) arrival in Europe, I've taken a first-time traveler to Brussels as a layover b/n Paris and Bruges. We put our luggage in storage at Centraal/Central Train Station and spent an hour or two wandering to and in Grand Place. Just allow time to return to the train station in plenty of time to make your Thalys train to Paris, find the luggage storage lockers, and retrieve your luggage.

I pretty much always gamble and buy my cheap tickets; if I miss my train, the loss isn't enough to get wound-up over, and if I make it it's a heck of a savings over full, walk-up fares. So far, so good...

Thanks for both responses. Yes, there's now a direct train from Brussels airport to Paris. But as far as I know, there's only one and it departs at 9:48am.

Thanks for the advice on advanced purchase. I'll probably do that, but am spending my last two nights in Brussels so will probably just leave enough time to grab a small bite and a coffee while trying to allow some time for a late arrival.

The fast train between Brussels and Paris is operated by Thalys, which operates like an airline. A ticket buys you a specific seat on a specific train. Your ticket acts the same as a seat reservation.

You can always buy tickets at the station, but you'll pay full price.