To investigate multiple facets of aggressive behavior, both directed at oneself and toward others, exhibited by patients suffering from mental illnesses, admitted to psychiatric units. Aggressive behavior is often seen in psychiatric inpatients, especially those with psychotic, substance abuse, and personality disorders. We conducted a literature search to collect information regarding these aspects, which then were summarized under several subcategories. We also included studies focusing on forensic psychiatric care units and aggressive events upon emergency room (ER) presentation. The most commonly used classification of aggression is the instrumental and reactive types, both defined by specific neurobiological changes. Several risk factors, such as younger age, being a male, having a history of adversity in early life, or having reported self-harm, are linked to a higher risk of aggression. The psychiatric pathologies that accounted for higher aggression rates were psychosis, and affective disorders, as well as those involving substance abuse, personality disorders, and intellectual disabilities. There are tools available for assessing aggression risk that could help with the prediction, avoidance, and management of such threatening events. Aggression and violence are linked to several psychiatric disorders. More effort should be directed to the training of the medical staff to effectively identify and manage threatening situations thus avoiding escalation and more traumatizing management measures.