Like other Slavic languages, Bulgarian lacked a definite article in its earlier stages. Unlike them, it has one today. The book formulates the rules that govern the use of articles and other markers of (in)definiteness in Modern Standard Bulgarian in comparison with the seventeenth century, and constructs a model of transition from the older system to the modern one, a model which is then evaluated against broader historical and dialect data and placed in a Balkan and general Slavic context.