This special issue is devoted to a refereed and edited selection of papers presented at the XVIth International Symposium on Night and Shiftwork held in Santos, Brazil, in November 2003. The journal Chronobiology International has also an issue (volume 21, n. 6, 2004) dedicated to that Symposium. Held every two years, these symposia are organised under the auspices of the Working Time Society and the Scientific Committee on Shiftwork of the International Commission on Occupational Health (http://time.iguw.tuwien.ac.at/index.htm).