The typical process of editing content on the web is strongly moded. Authors are forced to switch between editing and previewing and publishing modes before, during, and after the editing process. This thesis explores a new paradigm of editing content on the web called seamless editing. Unlike existing techniques for editing content on the web, seamless editing is modeless, enabling authors to directly edit content on web pages without the need to switch between any modes. The absence of modes reduces the amount of cognitive complexity involved with the editing process. A software framework called Seaweed was developed for providing seamlessly editable web pages in any common web browser, and is shown that it can be integrated into any content management system. For the purposes of experimentation, the content management system WordPress was selected, and a plugin using the Seaweed framework developed for it that provided a seamlessly editable environment. Two experiments were conducted. The first study observed users with no or minimal experience with using WordPress, following a set of prescribed tasks, both with and without the plugin. The second study was conducted over a longer time period in a real-world context, where existing WordPress users were naturally observed using the plugin within their own blogs. Analysis of logged interactions and pre-questionnaires and post-questionnaires showed that, in both studies, the participants found the Seaweed software to be intuitive and the new way of editing content to be easily adaptable. Additionally, the analysis showed that the participants found the concept of seamless editing to be useful, and could see it being useful in many other contexts, other than blogs.