Personnel rostering has received ample attention in recent years. Due to its social and economic relevance and due to its intrinsic complexity, it has become a major subject for scheduling and timetabling researchers. Among the personnel rostering problems, nurse rostering turned out to be particularly complex and difficult. In this paper, we propose a notation for nurse rostering problems along the lines of the ?|?|? notation for scheduling. The system allows extension as well as refinement. It is the aim of the notation to facilitate problem description, classification and systematic study. It enables authors to position the problems in the vaster body of research on the subject. By developing this notation for nurse rostering, we hope that an extension of it will be applicable to a broader domain of personnel rostering.