Edge is defined as the boundary pixels that connect two separate regions. Edges are local changes in the image intensity. Edges characterize boundaries and are therefore a problem of fundamental importance in image processing.. Edge detection plays a very important role in image processing The edges detected by algorithms are used by advanced computer vision,medical field,Brain Tumor detection,geologic formation extraction,biometrix and many more fields.In this article we are going to survey various edge detection techniques such as sobel, Prewitt, Robert,, Marr Hildrith and Canny operators.Althought each edge detection technique has its own merits and limitations .In this paper we would like to present various edge detection techniques with emphasis on Canny because the performance of canny edge detection technique is judged as the best in the field of image processing.