A syntactic-semantic investigation of subjunctive and indicative "da"-complements in Serbian is conducted in this project. After a careful comparison of Serbian sentence constructions with "da"-complements to the equivalent sentence structures in languages of the Balkans as well as other Slavic languages, it is clearly established that Serbian examples demonstrated a need to differentiate between indicative and subjunctive "da"-complements. In this thesis, a careful review of the basic verbal and sentential categories is presented following an overview of the literature which summarizes previous approaches to analysis of "da"-complements and introduces the main theoretical approaches within which the research is conducted in this thesis. Specifically, categories of verbal aspect, mood and tense are introduced as they are primary concepts which contribute to analysis of "da"-complements provided in this project. In addition, an overview of dependent as well as independent "da"-constructions is provided although the investigation is centered on dependent "da"-constructions. Semantic analysis of "da"-complements clearly suggests that aspect and tense are crucial categories that establish division between subjunctive and indicative "da"-complements in Serbian. In addition, clitic placement, negation interpretation, and licensing of negative polarity items further prove that subjunctive and indicative "da"-complements are introduced with homophonous "da". In syntactic analysis, by postulating different functional projections for two "da"(s), one which introduces indicative complements and another which introduces subjunctive complements, it is proposed that aspect and tense projections, clitic placement, negation interpretation, and licensing of negative polarity items in indicative and subjunctive "da"-complements could only be understood properly if the notion of two "da"(s), the indicative and subjunctive, is adopted. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]