Anyone who resides or works in the Netherlands is required, under the Health Insurance Act (Zorgverzekeringswet), to enrol with a health insurer to cover medical expenses within four months of arrival. The Dutch healthcare system is based on the principle of social solidarity. This means that healthy people contribute to the medical expenses of those who are ill. If you have an income or receive a social security benefit, you are also due to pay an income related premium, which will be deducted from your salary automatically. Depending on your situation, the percentage varies.
Extensive independent information by the Ministry of Health, Welfare and Sports about Health Care Insurances in English, German, Spanish, French and Polish can be found at the Zorgverzekeringslijn website. Their Healthcare Insurance Line (Zorgverzekeringslijn) can be reached at 0800-6464644 from within the Netherlands or +31-88-9006960 from abroad (9am to 5pm).
For students different terms and conditions might apply.
Another independent source of information is this government website.