Colonoscopy has an important role in the assessment of colonic symptoms and screening for colorectal cancer. Studies suggest that the quality of colonoscopy is variable. The focus of this thesis is improvement of colonoscopy quality, in particular patient comfort and polyp detection which are both important measures of colonoscopy quality. The studies within this thesis examine current medication practices and attitudes towards these and then assess whether simple interventions can improve the quality of colonoscopy. Discomfort during colonoscopy is common and influenced by many factors including the use of medication but practice varies between colonoscopists. Chapter three examines the relationships between medication practice and patient comfort during colonoscopy examinations performed within the English Bowel Cancer Screening Programme. Wide variation in patient comfort and medication use between colonoscopists are noted but with little apparent correlation. Deficiencies in the measurement of patient comfort are highlighted and strategies for improvement are suggested. Many strategies are available to manage discomfort during colonoscopy. Entonox (50:50 combination of nitrous oxide and oxygen) has advantages associated with its rapid elimination but is used in only a minority of examinations. Chapter four examines perceptions and attitudes towards Entonox use among English Bowel Cancer Screening Colonoscopists and explores whether these may explain its low utilisation. Attitudes towards Entonox use varied widely but were generally positive although it appears that Entonox is often selected for patients expected to have little discomfort. Colonoscopists’ attitudes towards Entonox use did not appear to explain its low utilisation. The method of Entonox use during colonoscopy varies between previous studies. Obstetric studies report that the method of Entonox use may influence its efficacy but this had not been examined during colonoscopy. The efficacy and side effects of ‘continuous’ versus ‘as required’ Entonox administration were compared in chapter five. Continuous Entonox administration did not increase potency but was associated with an excess of side effects. Despite colonoscopy being the gold standard technique to examine the colon, polyps may be missed. This is of paramount importance since polyp removal is associated with colorectal cancer prevention. Optimising polyp detection is therefore an important aim of colonoscopy. Polyp detection is influenced by bowel cleanliness. There are many bowel-cleansing agents available including low-volume bowel preparations, which have been advocated as a means to improve patient experience, but their effect on bowel cleanliness is debated. A comparison of bowel cleanliness following a low volume and standard volume bowel preparation before screening colonoscopy is detailed in Chapter six. Minor differences in efficacy were found between bowel preparations in a single colonic segment but there were major differences according to whether the bowel preparation was administered as a single or split dose. Previous studies have suggested position change may aid polyp detection but results are conflicting. Chapter seven compares routine patient position change, during colonoscope withdrawal, versus withdrawal in the supine position throughout. Routine position change significantly increased polyp and adenoma detection in the right colon. The studies within this thesis explore the utility of simple interventions that could easily be adopted by all colonoscopists, and may therefore lead to changes in practice that improve colonoscopy quality.