Humor has long enjoyed popularity among the scholars of various fields all over the world. The traditional research focuses on the logic, the nature, the working mechanism of humor and the rhetoric it employs. It finds that the logic in humor is quite different from that in serious discourses. The pragmatic research holds that humor results from the violation of the maxims of Grice's Cooperative Principle (CP). Scholars like Raskin even have attempted to present the Cooperative Principle for Humor. And the cognitive study suggests that speakers of humorous remarks violate the Relevance Principle (RP). They each can expound some types or some aspects of humor, but none of them can explain why speakers in humor would violate the normal logic or the principles of serious interactions. Furthermore, the abundant literature of humor, regarding its formation, its essence, the types and genres, its features and the topics concerned, seems to make the phenomenon too varied and too complex to grasp.The present study claims that humor is not a simple negation of serious communication, but that it follows an entirely different principle from that of serious discourses. Humor is multifaceted, but one thing is certain for all humor researchers, that is, humor is amusing. Amusement as the universal and essential element can be detected in diverse forms of humorous interactions. How do people amuse with words? Based on the argument of Speech Act Theorists that ‘utterances are actions', the study proposes that the speech act of amusement is performed through humorous remarks and is the basic unit of humorous interactions. The dissertation thus aims to reveal the essentialities of the multifaceted phenomenon with the focus on the amusing aspect of humor, by analyzing and describing the speech act of amusement performed in humorous interactions. The main part of the dissertation consists of Chapter 3 and Chapter 4. It distinguishes two communication modes: serious and humorous modes, and proposes that the constant mode-switching in communication leads to varieties of humorous interaction, with amusement as the universal and primary goal of communication. With Speech Act Theory as the theoretical guideline, the study then describes the speech act of amusement in terms of its components and its characteristics, and groups Amusement into the category of Directive Speech Acts. As an indirect directive speech act, Amusement is often made by an extended interaction called an ‘amusing' speech event with a central speech act of amusement to be inferred by recipients. The study finally extracts felicity conditions and a set of rules for Amusement. The constitutive rules are to be observed when the act of amusement is to be initiated, and the regulative rules determine the perlocutionary effect of the performed act of amusement.