The Essex National Mapping Project (NMP) has been carried out by Historic Environment, Essex County Council as part of the English Heritage National Mapping Programme. In Essex, the NMP contributes to the development of a broader historic environment record that includes historic environment characterisation and other thematic information. The project started in 1993, based on the well-established foundation of skills and data developed by Essex County Council since the mid-1970s. The project covered 190 Ordnance Survey 1:10,000 quarter-sheets and examined the available aerial photographs from several sources and archives for visible archaeological features. More than 10,700 archaeological sites have been mapped and recorded over the course of the project, of which 13.2% were new to the Essex Historic Environment Record. Much of the analysis has been carried out using GIS, which has allowed the archaeological features that have been mapped to be viewed in a landscape context and in conjunction with other geographical information such as geology, topography and historic mapping. This has aided the interpretation of features and allowed new classifications to be established.