The aim of this book is to present the experience and work carried out during a Mental Health and Psychiatric Nursing internship, as part of the acquisition of competences as a Specialist Mental Health and Psychiatric Nurse. To summarise, the work project is based on Betty Neuman's nursing model, and aims to develop a theoretical-practical work of empirical research and nursing intervention in the field of therapeutic adherence in people with mental illness, in Psychiatric Emergency and Psychosocial Rehabilitation contexts. The research is based on an extensive-quantitative strategy aimed at producing knowledge about the multidimensional systemic factors that underlie therapeutic adherence in people with mental illness. The central information-gathering technique was a questionnaire survey. The findings reveal that the presence of more severe psychotic episodes, with delusional activity and low insight, combined with weakened social ties, negatively influence therapeutic adherence