International bus services include services operated by both Busabout and Eurolines. While Busabout only stops in Amsterdam, Eurolines serves Amsterdam, Breda, The Hague, Rotterdam and Utrecht. Amsterdam is considered a major hub in the European bus network with bus departures for destinations throughout Europe and North Africa.
Because of the extensive rail network in the Netherlands, buses are often overlooked as a viable travel option within the country. However buses (operated by Connexxion or Interliner) are handy when combined with the train as a means to getting to some of the more out of the way places.
It is also possible to travel cross-country by bus, but as buses are primarily for travelling between small towns (rather than the larger cities), it can easily take twice as long as the same journey made by train. However it is a good option if you're interested in seeing the countryside.
Connexxion have a great value pass called Buzzer. For just €12 per day you get unlimited travel on Connexxion buses. It is valid after 9am Mon-Fri and all day on weekends.