This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book presents the exemplary research across a wide range of historical fields that have felt the impact of Geographic Information Systems (GIS) technologies and methodologies. It also presents six separate fields of historical research to demonstrate the impact of that new knowledge on historical understandings in a diverse collection of fields. These include population and demography, economic history, urban history, rural and environmental history, political history and the spatial humanities. The book illustrates the transformative impact of GIS on historical research. Historical GIS is a nomenclature within Spatial History that captures developments within geography in GIS and Geographical Information Science. GIS remains at the core of Spatial History. GIS is ultimately a database technology; it is distinctive because the information in databases developed for GIS includes geographical coordinates in addition to the data found in conventional databases.