Did you do a web search before you wrote that?

The first hit when I did:

http://www.iamsterdam.com/en-GB/living/official-matters/comp...

"In 2005 the Dutch government introduced a law to improve public safety stating that everyone must be able to produce valid identification when requested by the police or supervisory officials. Those who fail to produce vailid identification risk being fined. Read on to learn more about valid identification, and to whom the law is applicable."