Sleep and mood form a two-way circuit: disrupted nights amplify negative affect and impulsivity; depression, bipolar states, and anxiety in turn fragment sleep architecture and circadian timing. Sleep and Mood Disorders unpacks this loop so teams can diagnose precisely and intervene where it counts. We start with sleep physiology—homeostatic pressure and circadian rhythm gates—and how they shift across adolescence, pregnancy, and late life. Assessment goes beyond “how many hours”: ask about timing, regularity, chronotype, naps, caffeine, alcohol, nicotine, stimulants, pain, and screen exposure; screen for insomnia, hypersomnia, parasomnias, RLS/PLMD, OSA, delayed sleep–wake phase, and social jetlag. Psychiatric mapping matters: major depression often shortens REM latency and increases early-morning awakening; bipolar patterns can begin with reduced need for sleep; PTSD brings nightmares and hyperarousal spikes; ADHD frequently includes delayed sleep phase and inconsistent routines. We review first-line behavioral treatments—stimulus control, sleep restriction, circadian anchoring, light timing, exercise, and digital CBT-I—and pair them with pharmacologic options staged to diagnosis and risk. Antidepressants and mood stabilizers are chosen for night effects (sedation, activation, REM influence, weight, RLS) and for interactions with OSA or movement disorders. For OSA, we emphasize motivational onboarding to PAP, mask fit, desensitization, and weight or mandibular options; for nightmares, we cover imagery rehearsal and α-adrenergic strategies. Shift work, caregiving, and travel demand tailored plans: anchor wake time, pre-shift naps, light management, melatonin timing, and safety protocols. Measurement-based care keeps it practical: 2–3 minute scales, sleep diaries, wearable summaries, and weekly “energy–function” checks. Equity threads run through access to DCBT-I, PAP supplies, and language-matched coaching. When teams align sleep timing, light, and medications, Sleep and Mood Disorders, the discoverability of a sleep psychiatry conference, and core science like circadian rhythm become everyday tools to lift mood, cognition, and safety.