The progression of advanced disease often brings enormous adaptational challenges related to a loss of the capacity to be self-sufficient and to a heightened need for support from others. The increasing need to rely on others at the end of life may reactivate relational problems and may trigger threatening feelings of vulnerability and dependency. Clinicians may find it difficult to identify and respond appropriately to the specific relational needs of individuals receiving end-of-life care. Attachment theory is a developmentally-based approach to understanding the formation and maintenance of relationships relevant to felt security. Although attachment theory has been widely applied to parent-child relationships and to relationships of individuals with chronic medical conditions to their medical caregivers, it has not previously been applied to the understanding of clinician-patient relationships in the palliative care setting. This paper provides an overview of this theory and demonstrates its application and relevance to palliative care.