Bowel preparation is a core issue in colonoscopy,as it is closely related to the quality of the procedure.Patients often find that bowel preparation is the most unpleasant part of the examination.It is widely accepted that the quality of cleansing must be excellent to facilitate detecting neoplastic lesions.In spite of its importance and potential implications,until recently,bowel preparation has not been the subject of much study.The most commonly used agents are high-volume polyethylene glycol(PEG)electrolyte solution and sodium phosphate.There has been some confusion,even in published meta-analyses,regarding which of the two agents provides better cleansing.It is clear now that both PEG and sodium phosphate are effectivewhen administered with proper timing.Consequently,the timing of administration is recognized as one of the central factors to the quality of cleansing.The bowel preparation agent should be administered,at least in part,a few hours in advance of the colonoscopy.Several low volume agents are available,and either new or modified schedules with PEG that usually improve tolerance.Certain adjuvants can also be used to reduce the volume of PEG,or to improve the efficacy of other agents.Other factors apart from the choice of agent can improve the quality of bowel cleansing.For instance,the effect of diet before colonoscopy has not been completely clarified,but an exclusively liquid diet is probably not required,and a low-fiber diet may be preferable because it improves patient satisfaction and the quality of the procedure.Some patients,such as diabetics and persons with heart or kidney disease,require modified procedures and certain precautions.Bowel preparation for pediatric patients is also reviewed here.In such cases,PEG remains the most commonly used agent.As detecting neoplasia is not the main objective with these patients,less intensive preparation may suffice.Special considerations must be made for patients with inflammatory bowel disease,including safety and diagnostic issues,so that the most adequate agent is chosen.Identifying neoplasia is one of the main objectives of colonoscopy with these patients,and the target lesions are often almost invisible with white light endoscopy.Therefore excellent quality preparation is required to find these lesions and to apply advanced methods such as chromoendoscopy.Bowel preparation for patients with lower gastrointestinal bleeding represents a challenge,and the strategies available are also reviewed here. Bowel preparation is a core issue in colonoscopy, as it is closely related to the quality of the procedure. Patients often find that bowel preparation is the most unpleasant part of the examination. It is widely accepted that the quality of cleansing must be excellent to facilitate detecting neoplastic lesions. In spite of its importance and potential implications, until recently, bowel preparation has not been the subject of much study. the most commonly used agents are high-volume polyethylene glycol (PEG) electrolyte solution and sodium phosphate. There has been some confusion, even in published meta-analyzes, regarding which of the two agents provides better cleansing. It is clear now that both PEG and sodium phosphate are effective administered with proper timing. Conclusion, the timing of administration is recognized as one of the central factors to the quality of cleansing.The bowel preparation agent should be administered, at least in part, a few hours in advance of the colonoscopy. Severa l low volume agents are available, and either new or modified schedules with PEG that usually improve tolerance. Disease adjuvants can also be used to reduce the volume of PEG, or to improve the efficacy of other agents. can improve the quality of bowel cleansing. For instance, the effect of diet before colonoscopy has not been completely clarified, but an exclusively liquid diet is probably not required, and a low-fiber diet may be preferable because it improves patient satisfaction and quality of the procedure. Patients, such as diabetics and persons with heart or kidney disease, require modified procedures and certain precautions. Bowel preparation for pediatric patients is also reviewed here. Such cases, PEG remains the most commonly used agent. As detecting neoplasia is not the main objective with these patients, less intensive preparation may suffice. Specific considerations must be made for patients with inflammatory bowel disease, includingsafety and diagnostic issues, so that the most adequate agent is chosen. Identified neoplasia is one of the main objectives of colonoscopy with these patients, and the target lesions are often almost invisible with white light endoscopy. Herefore excellent quality preparation is required to find these lesions and to apply advanced methods such as chromoendoscopy. Bowel preparation for patients with lower gastrointestinal bleeding represents a challenge, and the strategies available are also reviewed here.