This book investigates nominal determination in Old English and the emergence of the definite and the indefinite article. Analyzing Old English prose texts, it discusses the nature of linguistic categorization and argues that a cognitive, usage-based construction grammar approach best explains when, how and why the article category developed. It is shown that the development of the OE demonstrative 'se' (that) and the OE numeral 'an' (one) should not be told as a story of two individual morphemes, but must be reconceptualized in constructional terms. The emergence of the morphological category 'article' follows from constructional changes in the linguistic networks of OE speakers and especially from 'grammatical constructionalization' (i.e. the emergence of a new complex schematic form-meaning pairing which previously did not exist in the constructicon). What has traditionally been interpreted as a case of grammaticalization involves changes on a more abstract, procedural level, involving constructionalization but also constructional competition. Next to functional reasons, the book especially highlights analogy and frequency effects as driving forces of linguistic change.