The Mental Status Examination (MSE) is a systematic assessment of a patient's psychological functioning at a specific point in time, analogous to the physical examination for medical conditions. The MSE evaluates multiple domains: appearance (grooming, hygiene, dress, psychomotor activity), behavior (cooperation, eye contact, agitation, catatonia), speech (rate, volume, tone, fluency, spontaneity), mood (patient's subjective emotional state -- asked directly) and affect (objective observation of emotional expression -- range, reactivity, congruence with mood), thought process (logical, tangential, circumstantial, loose associations, flight of ideas, thought blocking), thought content (delusions, obsessions, preoccupations, suicidal or homicidal ideation), perceptions (hallucinations -- auditory, visual, tactile; illusions; derealization), cognition (orientation, attention, concentration, memory, abstract thinking), and insight and judgment. The nurse documents findings using descriptive, objective terminology rather than diagnostic labels, distinguishes normal variants from pathological findings, correlates MSE findings with known psychiatric and medical diagnoses, recognizes MSE changes that indicate clinical deterioration (new psychotic features, worsening cognition), uses MSE findings to guide safety interventions (suicidal ideation requiring 1:1 observation), and communicates findings clearly during interdisciplinary handoff.