This systematic review examines the definitions of eHealth published between 1966 and June 2004. The term eHealth is widely used by various stakeholders, including individuals, academic institutions, professional bodies, and funding organizations. However, there is no universally accepted definition. The review identified 51 unique definitions, which covered a wide range of themes, including health and technology, commerce, activities, stakeholders, outcomes, place, and perspectives. Two universal themes were identified: health and technology. The definitions varied in length, with some as short as three words and others as long as 74 words. The review found that most definitions included the concept of health and technology, with some emphasizing the role of the Internet and other information and communication technologies. The definitions also varied in their focus, with some emphasizing the process of care and others focusing on the outcomes expected from eHealth. The review concluded that while there is no consensus on the meaning of eHealth, the term is widely understood and used. The review highlights the importance of communication among stakeholders and the need for further research to clarify the concept of eHealth. The review also notes that the term eHealth is often used in a broad sense, encompassing various aspects of health care, including health services, technology, and commerce. The review emphasizes the need for a more precise definition of eHealth to facilitate communication and research. The review also notes that the term eHealth is often used in a positive light, with many definitions suggesting that it can improve health care outcomes and increase efficiency. The review concludes that while there is no single definition of eHealth, the term is an important concept in health care and has the potential to improve health care delivery and outcomes.This systematic review examines the definitions of eHealth published between 1966 and June 2004. The term eHealth is widely used by various stakeholders, including individuals, academic institutions, professional bodies, and funding organizations. However, there is no universally accepted definition. The review identified 51 unique definitions, which covered a wide range of themes, including health and technology, commerce, activities, stakeholders, outcomes, place, and perspectives. Two universal themes were identified: health and technology. The definitions varied in length, with some as short as three words and others as long as 74 words. The review found that most definitions included the concept of health and technology, with some emphasizing the role of the Internet and other information and communication technologies. The definitions also varied in their focus, with some emphasizing the process of care and others focusing on the outcomes expected from eHealth. The review concluded that while there is no consensus on the meaning of eHealth, the term is widely understood and used. The review highlights the importance of communication among stakeholders and the need for further research to clarify the concept of eHealth. The review also notes that the term eHealth is often used in a broad sense, encompassing various aspects of health care, including health services, technology, and commerce. The review emphasizes the need for a more precise definition of eHealth to facilitate communication and research. The review also notes that the term eHealth is often used in a positive light, with many definitions suggesting that it can improve health care outcomes and increase efficiency. The review concludes that while there is no single definition of eHealth, the term is an important concept in health care and has the potential to improve health care delivery and outcomes.