Prison officers have been described as key determinants of the prison experience for prisoners, yet up until recently this occupational group was largely ignored in academic research. Although society often sees prison officers simply as ‘keepers of the keys’, the existing research has shown the job to be much more complex. In this book, the author explores an element of the prison officer’s job that is still understudied: the existence of ethical dilemmas. In doing so, this book highlights several questions: which ethical dilemmas do prison officers experience? How do they deal with them? Which values are important when dealing with ethical dilemmas? After discovering the answers to these questions, the author designs and evaluates an ethics training course for prison officers, in an attempt to increase their ethical competence, and the way they deal with ethical dilemmas. A second part of the book explores whether this training was successful and what can be learned from its implementation, not only for future training efforts, but also for the prison system in general. Het groene gras (‘the green grass’) is an academic book series on criminology (including security) that shares knowledge between scholars in The Netherlands and Belgium, offers a platform for young researchers and focuses on (comparative) research that is relevant for The Netherlands and Belgium. The series has a multidisciplinary approach, with a prominent place for criminology in relation to other disciplines. Publications in the series are in Dutch or in English.