This dissertation is a cross-linguistic investigation into the structure and interpretation of imperatives and related constructions. We identify universal morphosyntactic principles of imperatives and explain variations in the syntax of imperatives as a consequence of the interaction between the universal principles and the morphosyntactic system of a particular language. Based on these conclusions, we develop a model for the interpretation of imperatives. We show that the syntax of imperatives across languages includes an imperative operator, which is a set of morphosyntactic features. The interaction between a formal universal for the imperative operator and the syntax of a language correctly predicts the cross-linguistic variation in the availability of negative imperatives. We also account for the apparent peculiarity in the syntactic evolution of imperatives in the history of English. The results of our analysis confirm the postulated presence of an imperative operator and provide support for the presence of particular functional projections in the clausal phrase structure in English. We also propose that the morphosyntactic features of the imperative operator have interpretational consequences. We argue that the imperative operator includes a feature that encodes directive force, and another feature that encodes modality of unrealized interpretation. We also argue that subjunctives and infinitivals have an operator whose feature content is in a proper subset relation with that of the imperative operator. By defining the relation of imperatives, subjunctives and infinitivals in this way, we are able to capture the close relation that exists in many languages between these three types of sentences. We also account for the cross-linguistic variation in the syntactic behavior of the imperative subject by developing the idea that the imperative operator selects either an infinitive type or subjunctive type INFL, depending on the language. We define directive illocutionary force as an instruction to the hearer to update a PLAN SET, a set of propositions that specifies the hearer's intentions. Thus, the directive force of the imperative is not a result of inference; it is directly encoded in its logical form.