Multimodal discourse analysis has become an important current research topic in discourse analysis. There have emerged three theoretical approaches to multimodal discourse, namely the systemic functional-multimodal discourse analysis, the multimodal interactional analysis, and the corpus linguistic approach to situated discourse. The paper is intended to make a critical survey of the three approaches with the focus on their respective theoretical bases and analytical methods. The insights they offer into the features of human interaction and its research are discussed. The paper also explores the relevance of the three approaches to the study of multimodal situated discourse with reference to the research content, analytical categories and techniques.