With technological innovation, we now find that the use of digital means covers all areas including health, which is also moving towards the technological world. Electronic health is a term that refers to the use of information and communication technologies in health care. Indeed, the term does not only characterize technical development, but also a state of mind, a way of thinking, an attitude and a commitment to global thinking that aims to improve health care at the at local, regional and global levels and also to meet the needs of citizens, patients, professionals, health care providers as well as policy makers.

The sub-domains of electronic health
Digital health is a very broad field that encompasses a variety of subdomains such as:

1. Electronic health record systems
These are systems that systematically collect electronic health information for patients and store each action generated by one or more interactions in any healthcare environment.
This digitally stored information must be shared between different healthcare facilities to track patients wherever they go - specialist, hospital or even home - for better traceability.

An electronic health record (EHR) usually includes the following information:

◦ Patients data
◦ Medical history 
◦ Medications and allergies
◦ Vaccination Status
◦ Results of laboratory tests
◦ Radiological images
◦ Vital signs
◦ Personal statistics such as age and weight
◦ Progress notes and details of the problem
◦ Billing details

The EHR provides a complete view of the patient's health status, incorporating the patient's history, as well as feedback from all providers with access to the file. In contrast to paper files, EHRs optimize patient care by offering a number of benefits as they allow data to be tracked over time, including coordination of care, which optimizes the transition between settings. They also improve prevention efforts and the ability to identify missing information through better access to test results, reducing the need for redundant or unnecessary procedures.

Telemedicine is a medical act performed remotely by a doctor. In fact, it can be a consultation by video conference, a tele-assistance of a doctor during an intervention, a telemonitoring of the patient or a tele-expertise (exchange of the opinions of the doctors).

2.1. Teleconsultation
It is a consultation between a "teleconsultant" medical professional and a patient, who may or may not be accompanied by a health professional, through information and communication technologies.

2.2. Tele-expertise
The tele-expertise is the remote request by a health professional of a second medical opinion, thanks to the sending of images (scanner, radio, fund of the eye ...) and sometimes to the exchange by videoconference via Internet

2.3. Medical telemonitoring
Medical telemonitoring allows a doctor to remotely interpret the data necessary for the medical follow-up of a patient. It also makes it possible to take remote decisions concerning the care of people with certain diseases, elderly or with loss of autonomy and possibly to delegate actions to another health professional through a digital device.

3. M-Health (Mobile health)
Mobile health is the practice of practicing medicine and public and private health through mobile devices such as mobile phones, tablets and all devices that integrate with a mobile network. Mobile technologies are able to revolutionize the interaction of populations with health services. Mobile health has also been shown to facilitate access to health information, services and skills, and to promote behavioral changes that can prevent the occurrence of acute and chronic diseases. For example, patients receive and receive telephone calls or text / voice messages related to the observance of treatment or contacts with health workers, which greatly facilitates communication.

4. The use of Big Data systems
In the digital health sector, the term Big Data is the use of data science techniques to capture and analyze large and complex data in order to positively impact patient care outcomes and optimize business processes. The use of Big Data systems has emerged as the health sector produces large amounts of clinical, financial and administrative data that require large data-driven techniques to manage them. The use of big data is used to:

• Collect and consolidate large amounts of patient data from a variety of sources.
• Analyze the data collected for optimizing patient care.
• Apply the results of the data analyzed to improve the efficiency of patient care systems.

Overall, eHealth has become a network to deliver health services through digital technologies. Several activities are carried out in this sector using electronic media. This saves time, effort and allows for better communication. It has become the most modern approach to health care and affects a large number of patients and doctors around the world.