Abstract：The image edge is one of the most fundamental and significant features of the image. The edge contains a great deal of useful information on important contours and locations and offers people important parameters to describe and recognize objects in the image. Edge detection is one of the most basic operations in image processing, image analysis, and computer vision. It is one of the basic methods for pattern recognition and image information extraction. Research on edge detection has a long history, and there have been many algorithms proposed for it. However, all of the methods for edge detection still have some drawbacks and cannot detect the optimal edges in some cases. It is difficult to develop a general method for edge detection. Edge detection is a study hot spot in the field of image processing. New feasible theory and methods are proposed every day. The main research methods for the study of edge detection are to make improvements to existing methods or to find new methods for edge detection with special application requirements. This paper illustrates the significance of the edge detection and summarizes the elementary steps of edge detection and the general requirements for the obtained edge. Then it reviews the various methods of edge detection, analyzes the merits and the deficiencies of those methods, and summarizes the recent development of edge detection. Finally, it analyzes all kinds of common edge evaluation methods available at presently. This paper may serve as a valuable reference for future studies and applications of edge detection.