In patients with chronic constipation, identifying subtypes based on underlying physiology guides subsequent therapeutic choices. Chronic constipation subtypes include slow-transit constipation, pelvic floor dyssynergia, functional constipation, and irritable bowel syndrome with constipation. Chronic constipation subtypes are defined by the result of colonic transit, pelvic floor function, and the presence or absence of significant abdominal pain. Although a variety of tests are available, the most straightforward approach uses the 5-day colonic marker test of transit and anorectal manometry with balloon expulsion testing to evaluate for pelvic floor dysfunction. Patients with normal physiologic tests have either irritable bowel syndrome with constipation or normal-transit constipation. Significant overlap exists between subtypes and a clear distinction is not always possible, with up to a 50% overlap between patients with slow-transit constipation and irritable bowel syndrome, approximately 10% of patients evaluated exhibiting both slow transit and pelvic floor dyssynergia, and 50% of patients with pelvic floor dyssynergia also found to have slow transit. Symptom severity assessment provides the rationale for pursuing further testing and directing the aggressiveness of treatment as patients with greater symptom severity have reduced quality of life and poor physical functioning scores. Few constipation-specific validated measures exist for measuring symptom severity in chronic constipation. In clinical practice severity may be defined as mild symptoms having minimal impact upon daily activities or moderate to severe symptoms that increasingly interfere with daily life.