This book is a statistical study of Middle English prepositions. A detailed account of the occurrences of all prepositions in prose and poetry is given, including their dialectal and text-type distribution. All data are presented in abundant tables and figures. The analysis is based on textual evidence provided by more than 21, 000 samples extracted from the Helsinki Corpus of Middle English and the Middle English Dictionary. The study demonstrates how Middle English prepositions underwent semantic erosion, either via de-lexicalisation or through collocational and idiomatic processes. The influence of French in that semantic erosion is also dealt with, and illustrated with reference to French samples from the Analyse et Traitement Informatique de la Langue Française.