Historically, the Rhinelands refers (physically speaking) to a loosely defined region embracing the land on either bank of the River Rhine in central Europe. More recently the Rhineland (Rheinland in German) has become the general name for areas of Germany along the middle and lower Rhine in Germany between Bingen and the Dutch border, or between the confluence with the Neckar and Cologne. To the west the area stretches to the borders with Luxembourg, Belgium and the Netherlands; on the eastern side it only encompasses the towns and cities along the river. Except for the Saar this area more or less corresponds with the modern use of the term.

It is a contentious issue but between the two world wars the term "Rhineland" covered the whole occupied and de-militarized zone to the west of the Rhine including the bridge-heads on the eastern banks (see map below). After the collapse of the French dominated West Bank in the early 19th century, the German and Dutch (Province of Jülich-Cleves-Berg) speaking regions at the middle and lower course of the Rhine were annexed to the kingdom of Prussia. The Prussian administration reorganized the territory as the Rhine Province (also known as Rhenish Prussia), a term continuing in the names of the German states of Rhineland-Palatinate and North Rhine-Westphalia. Following the First World War of the early 20th century, the western part of Rhineland was occupied by Entente forces, then demilitarized under the Treaty of Versailles. German forces remilitarized the territory in 1936, as part of a diplomatic test of will, three years before the outbreak of the Second World War.