Much has been written about the history of Northern Ireland, but less well-known is its wealth of prehistoric sites, from which most of our knowledge of the early inhabitants of this country has been obtained. Until recently, the greatest sources for this information were prehistoric burial sites, which have been visible in our landscape for thousands of years and have attracted the attention of inquisitive people throughout this time, often removing items, or adding others and in doing so, making it difficult for later generations to sift through the evidence. Fortunately, sketches, notes and artefacts have been gathered by Ordnance Survey surveyors, antiquarians and archaeological and historical societies and these continue to be interrogated by modern archaeologists in their search for understanding. A further problem has been the dependence on information about prehistoric societies from their burial sites. Very few sites where these people lived and worked were visible above ground and as a consequence, little was known about them. However, during the last few decades, large-scale infrastructure projects and associated archaeological investigation has revealed a wealth of information. Much of the detail has still to be published and made available for research, but has already enriched understanding of our prehistoric past. This monograph brings together information on all the currently known sites in Northern Ireland that are in some way associated with prehistoric life. It has been compiled from a number of sources and includes many that have only recently been discovered. A total of 1580 monuments are recorded in the inventory, ranging from burnt mounds to hillforts. In addition to providing an inventory of all known sites, along with a selection of photographs and plans, the work also includes an introduction to the prehistory of Northern Ireland, an explanation of terms and a full bibliography. It should be considered alongside an earlier work by the same authors on prehistoric burial sites in Northern Ireland (The Prehistoric Burial Sites of Northern Ireland, Archaeopress Archaeology 2014). The aim is to provide a foundation for more specific research projects, based on a standardised format for this largely untapped resource and stimulate a renewed interest in the prehistory of Northern Ireland. Hopefully, this can then be considered along with our knowledge of the historical period to provide a more complete overview of the story of human activity in what is now Northern Ireland.