Colonoscopy is sometimes considered the preferred colorectal cancer screening modality, yet this modality may be subject to variation in operator performance more than any other screening test. Failures of colonoscopy to consistently detect precancerous lesions threaten the effectiveness of this technique for the prevention of colorectal cancer. Studies on high-level adenoma detectors under optimal conditions have begun to establish the true efficacy of colonoscopy and further widen the gap between efficacy and effectiveness. Research is required to establish the component skills, attitudes, and behaviors for high-level mucosal inspection competence necessary for training and assessment. Interventions to bridge the gap between efficacy and effectiveness are lacking, yet they should emphasize quality measurement and operate at various levels within the health system to motivate change in endoscopist behavior.