Paris to Bruxelles / Brussels by train

B-Europe is the website provided by Belgium's national railway operator for the sale of international rail journeys from and to Belgium.
Therefore tickets can be booked for the following international train services to/from Belgium

• Eurostar
• IC trains to France, Luxembourg and The Netherlands
• ICE trains to Germany
• Thalys trains to Germany, The Netherlands and Paris
• TGV trains to destination in France other than Paris
  B-Europe offers a 'Best Fares' policy for journey by these trains.

It also sells international end-to-end journeys solely by train, with connections outside of Belgium, if you will be heading to popular destinations in Austria, Germany, Switzerland and Italy.

Users of Eurail and InterRail passes can also book seat reservations on the Eurostar and Thalys services without paying booking fees.

SNCF is the national rail operator in France and not so long ago it recently simplified both the range of tickets and the term and conditions of using them.
Therefore the cheapest tickets also become more flexible too.

Other improvements included a simple integration of travelling with bicycles and rail pass users being able to book reservations for national journeys, without paying booking fees.

Though a legacy of when SNCF sold international tickets under the Rail Europe branding is that OuiSNCF is available in multiple translations with the offerings on the site then tailored to international visitors to France.
However, some of the site's features, including the integration of mobility assistance into the booking path, are only available on the French language version.

Something else to look out for is that simplest way of travelling with tickets is to use the SNCF 'My Travel' phone app, so it's therefore often a good idea to book on the OuiSNCF mobile service.

Happy Rail is a Netherlands rail ticket agency which sells tickets for both national and international journeys within a range of countries including Belgium France, Germany, Sweden, Switzerland.

HappyRail doesn't charge booking fees in the conventional sense, but if you're not Dutch you can expect to pay additional transaction fees, which will be added to the total cost.
That's because the most common form of online payment used in The Netherlands is 'iDEAL' and HappyRail doesn't charge a transaction fee for 'iDEAL' payments, but only Dutch residents can sign up to 'iDEAL'.
Other forms of payment include Visa debit cards will incur a fee.