Elena Badilla’s notebook is a private album dating from the beginning of the twentieth century that contains thirty-four pieces of sheet music for guitar. As well as pieces edited by renowned composers, it also contains some unpublished pieces apparently by Juan Guillermo Jara, a currently unknown composer. This article describes the advances that have been made in researching this source, exploring the social and cultural context of the guitar in Chile at the beginning of the twentieth century, with a specific emphasis on the city of Talcahuano, located to the south of Santiago. It also looks at the notebook as a material object, as well as carrying out a theoretical and musical analysis of the unpublished pieces initially attributed to Jara. The results shed light on guitar-related activity in the first decades of the nineteen hundreds.