In this article, it is argued that perfective aspect in Serbo-Croatian is licensed in the syntax. Licensing of Aspect requires the presence of a hierarchically higher category. In compound tenses, perfective aspect is licensed by a governing auxiliary in Infl while, in the present tense forms, it may only be licensed by an overt complementizer in Comp. A Comp-Aspect Agreement mechanism is proposed based on the requirement for licensing in the present tense forms. This agreement also obtains between a covert complementizer and perfective aspect in imperative constructions (perfective imperatives move to an empty Comp position to satisfy the Aspect licensing requirement) and between an overt complementizer and the auxiliaries in compound tenses (auxiliaries move to an empty Comp to satisfy the Tense licensing requirement). Although Tense may be licensed by any governor in root sentences, the presence of an overt complementizer, which is a hierarchically higher category, takes precedence for licensing in embedded sentences.