**1. Introduction**

This introductory chapter aims at presenting an overview of delirium in palliative care. In this setting, it is one of the most frequent, but often misunderstood and difficult to treat, symptoms. Moreover, this is a matter of paramount importance as delirium is associated with a heightened rate of falls, increased cognitive and functional damage, and important patient and family psychological discomfort. In these particularly vulnerable patients, distress expressed as a feeling of fear, anguish, humiliation — can be deleterious and is ethically unacceptable. Delirium is further associated with increased healthcare costs [1].

The term delirium derives from the Latin word deliria which literally means "to come out of the trace". It refers to a serious change in the mental state that leads to confusion and reduced awareness of the environment. This change is often accompanied by perceptual symptoms, such as hallucinations, or by cognitive symptoms such as disorientation and memory loss [2]. Nevertheless, rather than a symptom, delirium is a complex neurocognitive syndrome characterized by brain dysfunction with perturbations in the degree of consciousness, attention, thinking, perception, memory, psychomotor behavior, emotional sphere, and sleep–wake rhythm [3]. These clinical features differentiate delirium from a state of agitation that can be due to other undetected symptoms or physical needs (e.g., pain or full bladder).
