Notions of bowel habit lie in the eyes of the beholders. Constipation is one of the most difficult gut symptoms to define. Patients, physicians, and physiologists have different views of the condition. The difficulty lies in the many, but variably present, features of constipation. Since more than 98% of people have at least 3 bowel movements per week, less is often invoked as abnormal. Many manage happily with less, while others within that range are decidedly uncomfortable with what they believe is constipation. Reviewed and updated 2009.