Trust is an important factor to predict the behaviour of a Web Service and as a criterion for Web Service selection. Although considerable research has been performed in the offline and online worlds, analysis of trust in the Web Services environment has been limited. Most trust studies in Web Services are focused on trust establishment without identifying and considering the main trust definition components and trust principles. Thus, this paper presents trust definition and trust principles based on the exploration of the trust literature in the offline and online worlds and Web Services. The trust definition and principles form a basis to establish trust in Web Services.