This thesis shows how performance is a critically neglected but crucial aspect of serial television drama as an art form. One of serial drama's obvious storytelling attractions is its ability to involve viewers in relationships between characters over long periods of time. Such involvement takes place through a recurring structure of episodes and seasons, whose unfolding reflects the extensive, ongoing history through which interpersonal bonds form and develop, deepen and decay. The characters we watch onscreen are embodied and performed by actors. Television studies, however, has persistently overlooked screen performance, hampering appreciation of serial drama's affinity with long-term relationships as a resource for aesthetic significance. Redressing such neglect, this thesis directs new critical attention to expressive stylistic relationships between serial form, screen performance, and the subject of companionship in some recent US serial dramas.The focus of that attention is a particular aesthetic quality: the provisional, which emerges through serial drama's distinctive tension between permanence and transience. In the first chapter, I argue that the provisional is central to an affinity between screen performance, seriality in television drama, and companionship as an aspect of human life. Chapters Two and Three then show how the art of the provisional in particular series has been underappreciated due to television studies' neglect of performance and expressiveness as dimensions of serial form in television fiction. The final two chapters of the thesis highlight contrasting treatments of provisionality, performance, and the survival of social bonds in two critically celebrated US dramas of the mid-2000s: Mad Men (AMC, 2007-15) and Homeland (Showtime, 2011-19). In doing so, this thesis illuminates the significance and value to be found in an under-explored dimension of experience made available by performance in particular serial dramas. Its original contribution is to highlight overlooked features of this medium whose potential aesthetic significance should be a priority for the criticism of serial drama in television studies.