The rapid development of the Internet in the last decades has led to a new type of survey data collection: the web survey. Web surveys are becoming increasingly popular. This is not surprising. A web survey is a simple means of getting access to a large group of potential respondents. Questionnaires can be distributed at very low costs. No interviewers are needed, and there are no mailing and printing costs. Surveys can be launched very quickly. Little time is lost between the moment the questionnaire is ready and the start of the fieldwork. Web surveys also offer new,

attractive possibilities, such as the use of multimedia (sound, pictures, animation and movies).

So a web survey seems to be a fast, cheap and attractive means of collecting large amounts of data. This raises the question whether web surveys can be used for data collection in general population surveys. At first sight, web surveys seem to have much in common with other types of surveys. It is just another mode of data collection. Questions are not asked face-to-face or by telephone, but over the

Internet. There are, however, some methodological issues. Some of them are discussed here.