Convergence insufficiency (CI) is a well-known syndrome of binocular visual dysfunction. In a review of 58 papers, considerable variation was noted in the criteria used to define the condition. Symptoms and decreased positive fusional vergences (both at the nearpoint) were the only criteria named in more than one-half of the studies. An extended nearpoint of convergence (NPC) and increased exophoria at near were criteria in about one-third of the papers. Examination of data in the reviewed papers shows that although considerable variability was noted, the distance exodeviation, distance negative vergences, visual acuity, refraction, and stereopsis were about the same as population norms. Positive vergences, negative vergence at near, and NPC were somewhat less than population norms. Vergences relative to Sheard's criterion, the near exophoria, accommodative amplitude, and the AC/A ratio were consistently below those derived from population norms. This considerable variation may largely be a result of different criteria used for diagnosis, subpopulations within the data, and other confounding factors.