An internist is a physician who focuses on the diagnosis and treatment of conditions that affect the adult population—both acute and chronic.
These doctors are often who adults see as their primary physicians because they treat a broad range of illnesses that do not require surgical or specialist interventions. They also work to help a patient maintain optimal health in order to prevent the onset of disease.
In addition to treating the common cold and flu, internists also treat chronic diseases like diabetes and heart disease.

An endocrinologist is a physician with extensive training in understanding, diagnosing and treating conditions related to the endocrine system. The endocrine system regulates the balance of hormones.
Conditions of the endocrine system involve an over-abundance, or deficiency of a certain hormone. While there is a range when it comes to the amount of a hormone that is deemed normal in a human, these specialists determine whether a person's amount of hormone is indicative of a health concern. Two conditions this specialist might treat are diabetes and obesity.

An obstetrician & gynecologist, or OB/GYN, is a physician who cares for women throughout their pregnancies, straight through to the delivery of their baby (obstetrician). They also specialize in annual care, as well as the diagnosis and treatment of disorders of the female reproductive system (gynecologist). Many physicians specialize in both of these fields in order to provide complete overall health services to women at every stage of life.

A family practitioner is a doctor who specializes in caring for people of all ages, at all stages of life. Rather than focusing on the treatment of one disease or patient population, family practitioners are often the doctors that people see for their everyday ailments, like cold and flu or respiratory infections, and health screenings. When necessary, family practitioners will provide referrals for conditions that require the expertise of another specialist.
The doctors may also provide physicals, inoculations, prenatal care, treat chronic diseases, like diabetes and asthma, and provide advice on disease prevention.