Almost every survey suffers from nonresponse. Nonresponse rates are particularly high for voluntary surveys. The problem of nonresponse is that it affects the representativity of the survey results, and therefore causes estimates to be biased. Theoretically, it is possible to correct these estimates, but this requires sufficient auxiliary information. Unfortunately, such information is not always available. This paper discusses a number of issues and developments, based on a number of publications in the last decennium.