http://en.wikipedia.org/wiki/Dutch_nationality_law

Naturalisation as a Dutch citizen
An application for Dutch citizenship by naturalisation must meet all the conditions below:
*aged 18 or over;
* holder of a permanent resident permit;
*5 continuous years residence in the Netherlands, the Dutch Antilles or Aruba with a valid residence permit. There are a number of exceptions to this rule.
*sufficiently integrated in Dutch society and are able to read, write, speak and understand Dutch. This must normally be proved by taking a naturalisation test. Successful completion of an eligible integration course is an alternative.
*in the four years preceding the application, the applicant has not been given any custodial sentence, training order, community service order or high monetary penalty.