Constipation is a common problem in patients with advanced cancer and a significant source of major morbidity and distress, which is often under-appreciated. Constipation is subjectively experienced by the patient and diagnostic criteria do not always clearly express the diversity of factors, which may lead to constipation as a clinical problem. Widespread use of opioid analgesics for cancer pain poses specific challenges for patients. Despite its clinical impact, constipation is both poorly recognised and poorly treated. Oncologists must be familiar with the common causes of constipation among cancer patients and the strategies to evaluate and manage this distressing symptom. This European Society for Medical Oncology (ESMO) Clinical Practice Guideline (CPG) is directed towards adult cancer patients experiencing constipation as a consequence of their cancer diagnosis or treatment. The CPG makes specific reference to the context of opioid-induced constipation (OIC), highlights the impact of constipation and offers strategies for pharmacological and non-pharmacological management, as well as the specific challenges in the management of older patients with cancer at enhanced risk of constipation.