This book addresses the problems of the nature of the category of aspect, its formal expression and its relation to Action modes, to the Aorist/Imperfect and Perfect/Non-Perfect distinctions. The discussion is largely based on data from Bulgarian -- a Slavonic language where aspect as a grammatical category systematically coexists not only with verbal prefixation, but also with temporal boundedness, correlation and, in the nominal sphere, definiteness. Cross-language parallels with English and French data and the mapping of Bulgarian structures to notions drawn from the «western tradition of aspectual study result in the outline of a framework for an integrated study of the expression of aspectuality in languages belonging to different language groups. Refuting existing views of aspect as a «compensatory phenomenon for nominal definiteness, the book presents arguments in favour of a systematic relation between verbal prefixation and NP quantification in Slavonic languages and of a compositional, syntactic dimension of aspectual analysis.