This book presents the results of a corpus-based case study of diachronic English syntax. Present Day English is in a minority of European languages in not having a productive dative external possessor construction. This construction, in which the possessor is in the dative case and behaves like an element of the sentence rather than part of the possessive phrase, was in variation with internal possessors in the genitive case in Old English, especially in expressions of inalienable possession. In Middle English, internal possessors became the only productive possibility. Previous studies of this development are not systematic enough to provide an empirical base for the hypotheses that have been put forward to explain the loss of external possessors in English, and these earlier studies do not make a crucial distinction among possessa in different grammatical relations. This book traces the use of dative external possessors in the texts of the Old and Early Middle English periods and explores how well the facts fit the major proposed explanations. A key finding is that the decline of the dative construction is visible within the Old English period and seems to have begun even before we have written records. Explanations that rely completely on developments in the Early Middle English period, such as the loss of case-marking distinctions, cannot account for this early decline. It does not appear that Celtic learners of Old English failed to learn the external possessor construction, but they may have precipitated the decrease in frequency in its use.