Television is in a period of dramatic change. As the mass audience continues to fragment into ever-smaller niche audiences and communities of interest, and new technologies shift control over the television viewing experience from network programmers into the hands of media consumers, television’s traditional business models prove themselves increasingly untenable. In an attempt to preserve these models, television executives are attempting to shed television’s long-standing reputation as a passive medium, which emphasized the viewer’s role as a consumer of television content, and which critics often decried as vacuous and mindless. The current discourse suggests that television’s future now relies on the industry’s success recasting it as an active medium, capable of capturing and holding the audience’s attention, and effective at generating emotional investment. The single most important concept in this new industrial discourse is that of audience “engagement”, a term that has generated a tremendous amount of debate and disagreement, with television and advertising executives alike struggling to understand what engagement is, how it works, and what its practical consequences will be. This thesis argues that television’s future as an engagement medium relies not on inventing new methodologies that define engagement in terms of quantifiable audience behaviors and attitudes, but instead in a new conceptual model of television, better suited to a multi platform media environment and the emerging attention and experience economies, which focuses on the development of television programs that extend beyond the television set. Such a model must understand television not as a method for aggregrating audiences that can be sold to advertisers, but as a medium that draws upon media platforms, content, products, activities and social spaces to provide audiences with a range of opportunities to engage with television content. Accordingly, this thesis offers a framework for thinking about viewer engagement as the range of opportunities and activities that become possible when drawing upon an expanded, multi-platform conception of the modern television text. Applying this framework to the innovative and experimental textual extensions developed around ABC’s Lost, the thesis indicates both the challenges and opportunities that emerge as television becomes an engagement medium.