The Senate Select Committee on Intelligence found that the Russian government engaged in an aggressive, multifaceted effort to influence, or attempt to influence, the outcome of the 2016 presidential election. Parts of this effort are outlined in the Committee's earlier volumes on election security, social media, the Obama Administration's response to the threat, and the January 2017 Intelligence Community Assessment (ICA). This fifth and final volume focuses on the counterintelligence threat, outlining a wide range of Russian efforts to influence the Trump Campaign and the 2016 election. In this volume the Committee lays out its findings in detail by looking at many aspects of the counterintelligence threat posed by the Russian influence operation. For example, the Committee examined Paul Manafort's connections to Russian influence actors and the FBI' s treatment of reporting produced by Christopher Steele. While the Committee does not describe the final result as a complete picture, this volume provides the most comprehensive description to date of Russia's activities and the threat they posed. This volume presents this information in topical sections in order to address coherently and in detail the wide variety of Russian actions. The events explained in these sections in many cases overlap, and references in each section will direct the reader to those overlapping parts of the volume.