Adequate cleansing of the bowel is important for a reliable and diagnostic colonoscopy. Proper bowel preparation is directly correlated to the diagnostic performance of colonoscopy, procedure time, cost price and the complication rate. The ideal bowel preparation agent should be efficient, safe and well tolerated by the patient. Numerous agents have become commercially available overtime. Current agents can be classified according to their tonicity, as being isotonic or hypertonic. Poly-ethylene glycol based solutions balanced with electrolytes are the prototype of isotonic bowel preparations. Poly-ethylene solutions are safe and efficient in cleaning the bowel. Volume related side-effects are common, leading to innovations such as split dosing, and low volume solution combined with another laxative. Sodium phosphate and magnesium oxide are hypertonic agents. They are efficient and well tolerated, but safety issues regarding sodium phosphate has hampered its success. Because most physician are likely to prescribe bowel preparation agents for colonoscopy, they should be aware of the range of preparations commercially available and their limitations. This review focuses on the efficacy, tolerability and safety of current available bowel preparation agents.