Chapter 5 introduces monitoring as a technique that enables changes in coastal landscapes to be identified and evaluated over time. To assess change, it is necessary to have a baseline dataset recording the historic configuration of coastal features against which change can be measured. Baseline datasets should be reliable and in a comparable frame of reference, and may include maps, aerial photographs of satellite images. It is only possible to attribute the difference between a contemporary map and a historical one to coastal change that has occurred if the magnitude of the difference exceeds the uncertainty associated with both the mapping and comparison methods. Coastal change can be measured using raster and vector datasets. The success of a change detection exercise depends largely on the nature of the change being observed and the pairing of this with a suitable technique for its detection. Sources of error in change detection include the data used, its format and georeferencing, comparison of information in different frames of reference (projections, datums) and inaccuracies in digitising (vector) and classification (raster).