The achievement of low fiber optic interconnection losses depends upon precise fiber alignment, and on the quality of the fiber end faces. This paper is concerned with end face quality as obtained through the use of fiber cleaving tools. High quality end faces require careful design and use of cleaving tools. The factors affecting end face quality are addressed, including scribing, tensile force and twist angle. Deviations from optimal conditions produce a number of different types of defects. A basic requirement for low interconnection loss is that the end face be nearly perpendicular to the fiber axis. The fiber end angle relative to the ideal plane can be minimized by attention to the methods used for clamping the fiber and for applying the tensile force. In addition to the end face angle, a number of other defects are identified, including hackle, mist, cracks, lips, breakover, and chips. These defects are related to the manner in which the scribing and cleaving are performed. The effects of the defect, as wen as the influence of index-matching media and fiber fusion on losses, are discussed. Some characteristics of commercial cleaving tools are given. Fiber Optic Test Procedures are being developed by the Electronic Industries Association (EIA) to identify and quantify fiber end face defects. Generic and Sectional Specifications are also being written for cleaving tools by the EIA FO-6.1 Subcommittee. These are major steps toward defining standards for quality of cleaved end faces.