Westphalia (in German, Westfalen) is a (historic) region in Germany, centred on the cities of Münster, Bielefeld, and Osnabrück and now included in the Bundesland of North Rhine-Westphalia (and the (south-)west of Lower Saxony).
Westphalia is roughly the region between the rivers Rhine and Weser, located north of the Ruhr river. No exact definition of borders can be given, because the name "Westphalia" was applied to several different entities in history. For this reason specifications of area and population are greatly differing. They range between 16,000 and 22,000 km² resp. between 4.3 million and 8 million inhabitants.
There was a kingdom of Westphalia from 1807 to 1813. It was founded by Napoleon and was a French vassal state.This state only shared the name with the historical region, it contained mostly Hessian and Eastphalian regions and only a relatively small part of Westphalia.
A linguistic definition of Westphalia includes the former Prussian province (except the Siegerland) and the region around Osnabrück. Present-day common use, however, restricts the notion to the present northern part of North Rhine-Westphalia, because of the name.