Behavioral and psychological symptoms of dementia (BPSD), constitute a major clinical component of Alzheimer's disease (AD). There is a growing interest in BPSD as they are responsible for a large share of the suffering of patients and caregivers, and they strongly determine the patient's lifestyle and management. Better detection and understanding of these symptoms is essential to provide appropriate management. This article is a consensus produced by the behavioral group of the European Alzheimer's Disease Consortium (EADC). The aim of this article is to present clinical description and biological correlates of the major behavioral and psychological symptomatology in AD. BPSD is not a unitary concept. Instead, it should be divided into several symptoms or more likely: groups of symptoms, each possibly reflecting a different prevalence, course over time, biological correlate and psychosocial determinants. There is some clinical evidence for clusters within groups of BPSD. Biological studies indicate that patients with AD and BPSD are associated with variations in the pathological features (atrophy, brain perfusion/metabolism, histopathology) when compared to people with AD without BPSD. An individually tailored approach taking all these aspects into account is warranted as it may offer more, and better, pharmacological and non-pharmacological treatment opportunities.