The growth of modern European nations and the spread of their languages have been parallel developments. This parallelism is founded on the material ties no less than on the spiritual affinity which bind men to the earth. To furnish evidence of this relationship lies within the province of geography. Historical testimony is also at hand to show that political and linguistic frontiers have tended to coincide during the past two centuries, except where artificial measures have been brought into play. Broadly it may be submitted that the advance of civilization in most countries has been marked by the progress of nationality, while nationality itself has been consolidated by identity of speech. Language areas, in common with many other facts of geography, have been largely determined by the character of the surface or climate. Occurrences such as the extension of Polish speech to the Carpathian barrier or the restriction of Flemish to the lowland of northwestern central Europe, are not the work of mere chance. An investigation of linguistic boundaries, therefore, implies recognition of the selective influence of surface features. But the influence of region upon expansion or confinement of language is far from absolute. The part played by economic factors will be shown in the following pages to have been of prime importance. Considered as political boundaries, linguistic lines of cleavage have two-fold importance. They are sanctioned by national aspirations and they conform to a notable degree with physical features. Every linguistic area considered in these pages bears evidence of relation between language and its natural environment. A basis of delimitation is therefore provided by nature. Eastern extension of French to the Vosges, confinement of Czech to a plateau inclosed by mountains, uniformity of language in open plains and river basins, all are examples of the evidence provided by geography for statesmen engaged in the task of revising boundaries.