The thesis "Building and exploiting context on the Web" presents several studies regarding the different aspects of context on the Web. Thorough studies are performed and presented in the thesis in order to understand the different aspects of context on the Web. In addition, several tools are proposed and developed to support contextualization in Web environments. Later, in each chapter, the benefits of exploiting different aspects of context is presented through a series of experiments and user studies. Finally, the thesis propose several future directions for improvements and envisages new possibilities for valuable contextualized web tools.