Psychiatric intensive care units (PICUs) treat patients with an acute episode of a major mental illness who present with additional risk of harm to themselves or others that cannot be managed on an acute psychiatric ward. This chapter outlines standards of care that are expected upon such units, what they are and how the standards were developed with clinical rationale. It also gives examples of other guidelines and standards that impact practice within a PICU setting. It also describes the process of quality improvement in such units and how this relates to continual positive progress within a PICU setting. It alludes to how the principles of psychiatric intensive care can be incorporated within other settings and the need for clear definition of subspecialities within psychiatry.