Dress is somewhat informal in comparison with countries such as the UK or Japan. To some extent, dress code is determined by industrial sector.
The more conservative areas such as banking tend to veer towards suit and tie whilst the newer industries take a more casual approach. Even the sectors with a more casual approach would, however, remain fairly smart.
As with the USA it is always a good idea to check before travelling. As the Netherlands suffers from a fairly heavy average rainfall figure, umbrellas and raincoats are often necessary.