If you're planning to book your tickets far in advance, you need to know that different European countries have different policies for when tickets go on sale. With us however, you can book your rail journey as far as 2 years in advance, and live your life with a peace of mind that your tickets will be issued on time once they are available. Here are some generic tips on when tickets usually go on sale:
For most Western European countries booking usually opens 90 (or 92) days ahead. For certain trains tickets go on sale up to 120 days ahead, for example: Paris - Milan or Paris - Barcelona routes, TGV-Lyria trains between Paris & Switzerland, and Italian domestic high-speed trains (unless it's a high season)
When buying tickets for Spain high-speed AVE trains, tickets are usually open for reservation 90 days prior to departure date. For non-AVE trains, tickets become available 60 days ahead. However remember, these numbers are not always exact! For example, Renfe opens blocks of dates at a time following their own logic which does not always correspond with the numbers above.
For most Russian trains tickets are available 59 days prior to departure. For international routes bound to Russia (like Helsinki - St. Petersburg) tickets may be open for booking up to 60 days ahead.