This book analyses the relationship between digital media systems and post truth politics. It demonstrates that the complexity of modern systems is an existential challenge for our ability to understand and research these issues. A new theory is proposed for studying complexity, explaining how system interactionism differs from established ideas, including assemblage and actor network theories. After considering the social system of Niklas Luhmann, the author proposes an interactionist methodology better equipped to deal with system complexity. A description of the logical operations of the digital and political systems is provided, establishing precedents for an analysis of the role of hypertext in shaping the emergent digital-politics. The book demonstrates how the principles of system interactionism can guide digital media research into polarisation and political language.