The following chapter focuses on the most important guerrilla group in the Colombian armed conflict in terms of significance and capabilities: the Revolutionary Armed Forces—People's Army (FARC-EP). To this end, it looks at its particular origins and the elements that organised its first steps as an insurgent project. Likewise, special attention is paid to the profound transformations experienced in the eighties and nineties when the FARC-EP even had real capabilities to confront the Colombian State militarily. Also, its sources of financing and its main territorial anchors, in order to observe its logic of action, especially coinciding with the turn of the millennium and the arrival of Álvaro Uribe to the presidency. With the above, we will attempt to explain the elements of the rise of the confrontation and subsequent dialogue and demobilisation that took place between 2010 and 2017.