Colonoscopy is an invasive, endoscopic procedure undertaken to visualise the inner lumen of the colon and is used for a variety of diagnostic purposes. The procedure is increasingly performed by nurse endoscopists. This article provides an overview of the indications and contraindications for colonoscopy and describes various elements of the procedure, including consent, sedation and bowel preparation within the context of the evidence base. The article also discusses patient care before, during and after the procedure.