Trustworthiness is one of many aspects that affect the construction of mutual trust. Mutual trust is essential for smooth and successful collaboration in the social systems that people navigate as part of their professional lives and in private settings. Trustworthiness is therefore a concern for all members of society. If trustworthiness is a participant's concern and interactional project, it should be possible to trace it in authentic recordings of social interaction. Academic fields which have traditionally been concerned with trustworthiness includes the social sciences, especially sociology, economics, political science and psychology; business and management; philosophy; and rhetoric. The chapter also presents an overview on the key concepts discussed in this book. The book explores interactional strategies and moves that may indicate trustworthiness as a member's concern in social interaction.