Mental health nursing integrates biological understanding of psychiatric disorders with therapeutic communication, milieu management, and safety principles. Therapeutic communication is the foundation of psychiatric nursing care: techniques include active listening, reflecting feelings, restating/paraphrasing, exploring, focusing, presenting reality (for hallucinations — without arguing), and offering self. Non-therapeutic responses to avoid include: giving advice, false reassurance ('everything will be fine'), asking 'why' questions (perceived as judgmental), changing the subject, and agreeing with delusions. The nurse maintains professional therapeutic boundaries — the relationship exists for the patient's benefit, not the nurse's. Boundary crossings (minor deviations that may benefit the patient) differ from boundary violations (exploitation of the nurse-patient relationship). Milieu therapy provides a structured, safe, therapeutic environment with predictable routines, clear expectations, and group activities. The nurse manages the milieu by ensuring environmental safety (sharps removal, ligature risk assessment, elopement prevention), implementing least restrictive interventions (de-escalation before medication, medication before restraints), and maintaining a safe space for patients. Legal and ethical principles include informed consent, right to refuse treatment, involuntary commitment criteria (danger to self, danger to others, gravely disabled), patient rights in...