In recent years, there has been an explosion of interest in the possibility of early intervention (EI) in mental health care, with the ultimate aim of preventing the onset of severe mental illness, or at the very least, preventing or reducing the secondary morbidity and impaired functioning associated with these illnesses. This has been largely driven by advances in our understanding of the early stages of the psychotic disorders, which have led to the identification of modifiable risk/protective factors that can be targeted by appropriate therapeutic interventions, leading to much better outcomes for affected individuals and their families. EI represents a key shift in theoretical perspective, providing a coherent focus for the timely prevention, detection, and intervention in mental illnesses, and opens the way for a more congenial, pre-emptive or timely, and ultimately, more personalized and preventive psychiatry. This shift in focus and perspective must be reflected in the timing, pattern and tenure of service delivery, as well as in service structures themselves. In this chapter, we review the EI paradigm as a rationale and framework for improving the systematizing of evidence-based primary to tertiary preventive efforts and the responsiveness of mental health services for individuals with many types of significant psychiatric disorders and their families, in most age-groups and settings. We address some key questions: Is EI anything really new? Should it only be for young people with psychosis? Should the work of EI teams be time-limited? Can there be an EI approach to long-term or persistent disorders? Can EI be applied to enhancing wellness and wellbeing? We also address the need for and uses of tools of EI service quality, from values and principles, to standards, accreditation, best practice and implementation guidelines and similar applications of fidelity criteria. We finally summarize the overall benefits of taking an EI approach, as potentially one of the most important advances in mental health care made in recent years.