Eurolines is the main ‘operator’ for international coaches to the Netherlands. (In fact the name Eurolines is a common brand-name used by different operators). Services are limited: only a few main routes have a daily service, such as from Poland, London, Milan, Brussels and Paris, but this is the cheapest way to travel and you get a discount if you are under 26 of age.
PublicExpress runs a line from Bremen via Oldenburg to Groningen.
Due to the Bosnian war in the 1990s, there are bus companies serving the Bosnian diaspora, which provide a cheap and clean way of getting to the other side of the European continent. Semi tours runs several times per week from various destinations in Bosnia and Herzegovina to Belgium and the Netherlands, Off-season approx. 135€ for a return ticket.