Book excerpt: This text provides an accessible and up-to-date introduction to criminal justice for all those undertaking degrees and foundation degrees in policing. It will also be relevant to degree courses in criminology and criminal justice. The book provides a holistic overview of the Criminal Justice System (CJS) and an exploration of the roles of key players within the system and how the police interact with these organisations. It examines some of the principles that underpin the ′modernisation′ of the police, in particular how the police service collaborates with partner agencies and the rationale associated with the Change Agenda.