Pick your carrier to Belgium. French TGV trains offer services to Belgium; ICE trains travel from Germany to Belgium; Thalys links Amsterdam, Cologne and Paris to Brussels; Eurostar offers trains from London or Paris; Eurail offers a Benelux pass, which gives travelers access to Belgium from the Netherlands and Luxembourg; and booking through the Belgian Rail Road allows you to book from anywhere in Europe.
Pick your departure city and the arrival city in Belgium to search for tickets.
Book online by entering your credit card information, or just show up to book at major stations throughout Europe. Many connections are available daily, so advance planning is not mandatory.