This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book discusses how none of the preeminent models have been independently and robustly evaluated under a sufficient array of conditions. The relationship between policing and mental health is changing. The publication of groundbreaking academic studies is helping practitioners and policy makers to better understand various aspects of mental health. Police services across the United Kingdom, Australia, the United States, Canada and other jurisdictions are actively sharing their experiences and understanding of ‘what works’ at the nexus of policing and mental health. Training regimes, funding of police staff levels and the resourcing of partner agencies are not the responsibility of frontline officers. Government bodies at the local and national level are almost entirely responsible for police funding and the financing of partner agencies. Police management and policy makers, in turn, are responsible for shaping and ensuring the quality of police training.