Medicine is the science that deals with diseases (illnesses) in humans and animals, the best ways to prevent diseases, and the best ways to return to a healthy condition.

People who practice medicine are most often called medical doctors or physicians. Often doctors work closely with nurses and many other types of health care professionals.

Many doctors specialize in one kind of medical work. For example, pediatrics is the medical specialty about the health of children.

In this specialty, the doctor is trained to provide anaesthesia and sedation. This is important for surgeries and certain medical procedures. Anaesthesiologists also provide pre-operative assessments, ensuring the patient is safe during the operation and successfully awakens from anaesthesia after the operation. They assess for medical conditions and suitability for anaesthesia. They screen for risk factors prior to surgery and try to optimize the operative environment for the patient and the surgeon. They are the doctors who give epidurals during labor and delivery, provide spinal blocks, local nerve blocks, and general anaesthesia for procedures. They are the doctors who are especially trained in intubation (putting a tube into the lungs to help a person artificially breathe when the person is paralyzed and asleep during surgery). Hence, due to their skill in intubation, they are often the first line responders for emergencies. They help people who are in distress with their breathing, who have lost their airway or when their airway has become obstructed.

A cardiologist is a doctor with special training on the heart. The doctor in this field ensures the heart is healthy and functions properly. The heart is a vital organ whose role is to pump blood to the rest of the body. The purpose of blood is to deliver oxygen to the tissues. Without the heart functioning well, our tissues and organs would die and not function properly. Cardiologists treat heart attacks, sudden cardiac arrests, arrhythmias (rhythm issues related to a faulty electrical system of the heart), heart failure (where the heart fails to pump blood forward properly) and many other heart related illnesses. They specialize in life saving procedures like cardiac stents and cardiac ablation. There is a subspecialty within cardiology called "Interventional cardiology." These are cardiologists who specialize in interventions or procedures to save the function of the heart, such as cardiac stenting or angiography.

This specialty consists of well trained doctors who practice cardiac surgery. They are best known for their role in cardiac bypass surgeries. In cardiac bypass, the surgeon restores blood flow to the area of the heart that was deficient due to a blocked coronary artery. This is usually done by taking a vein, most commonly the saphenous vein from the leg, to create a pathway of blood flow to the heart region that needs it.

Emergency room doctors are in charge of sudden important or life-threatening emergencies. In addition to dealing with heart attacks, strokes, traumas, issues that require immediate medical attention or surgeries, they also deal with a wide range of other health conditions, such as mental health and drug overdoses. Their training is broad and diverse as anyone can walk through the door seeking help. They see patients of all ages and walks of life. However, unlike a general practitioner or family doctor, their immediate goal is to make sure the patient is stable and exclude any serious or life-threatening diseases or conditions.

A family doctor, otherwise known as general practitioner, is trained to provide medical service to people of all ages, demographics, and walks of life. Their training is diverse to deal with a variety of conditions including all non surgical specialties. They also follow the patient from birth to death and are trained to treat an individual as a whole, in the context of their social setting and also their family situation and mental health. Unlike specialists who mainly deal with problems of one organ or system, family doctors deal with all parts of the body and synthesize this information for the patient's general health. They provide a global perspective of the person's health in the patient's unique life situation. They are an individual's regular doctor who knows the patient in their social and family context. They can refer to specialists for issues that require more detailed or specialized treatments unavailable to them as an outpatient or beyond their expertise.

Gastroenterologists are doctors who specialize in the gastrointestinal (GI) tract and upper abdominal organs. The GI tract is consists of the esophagus all the way down to the anus. The upper abdominal organs include the liver, gallbladder, pancreas and spleen. In addition to dealing with medical conditions associated with these organs, doctors in this speciality also perform endoscopies. This is where a camera is placed to visualize the esophagus and stomach (upper endoscopy) or the colon (lower endoscopy or colonoscopy). Gastroenterologists that specialize in the liver is called a Hepatologist. They are responsible for treating patients with liver failure or cirrhosis. They also treat patients with viral Hepatitis (A,B,C) and many other forms of liver disease.

Doctors in this specialty are trained to recognize and treat a variety of different conditions involving the internal organs. They have wide knowledge in a number of specialties including, but not limited to: Respirology, Nephrology, Gastroenterology, Cardiology. Doctors who practice broadly in this field are known as General Internists (or General Internal Medicine doctors). Internists can go to receive further training beyond residency in a particular field. For example, Gastroenterologists are internists that have chosen to specialize in GI medicine. Internal medicine doctors are in charge of inpatient units when patients are admitted for a general reason. Unlike family doctors and emergency doctors, although their training is diverse and they have broad knowledge in many organ systems, they do not treat or manage children, babies, or pregnant women. (Those patients are instead cared for by Pediatricians and Obstetrics/gynecology, respectively.)

Doctors in this field, abbreviated OBGYN or Obs/Gyn, specialize in women's health covering conditions of the female reproductive organs, and pregnancy care and delivery. Some examples of gynecological issues they deal with include contraceptive medicine, fertility workup and treatments, prolapse and incontinence, sexual health, ovarian tumors/ cysts, gynecological oncology. They are also surgeons in their fields, capable of performing numerous gynecological surgeries. Doctors in this field also practice obstetrical medicine, specialising in maternal fetal care and deliveries, complications related to deliveries, assisted deliveries (such as vacuum and forceps deliveries) and Caesarian sections.

This medical specialty consists of well trained doctors who recognize and treat medical conditions associated with the eyes. Some common complaints they see include red eye, eye pain, visual changes and trauma. They deal with many eye diseases including conjunctivitis, iritis, blepharitis, hordeolum, chalazion, glaucoma, cataracts, macular degeneration, retinal detachments, papilloedema, central retinary artery occlusion.  They are trained to perform surgery.

These are doctors with special training to treat the ears, nose and throat.  These are the doctors who will very commonly remove an organ call the "tonsils" from a patient.

This medical speciality, commonly known as chest medicine or respiratory medicine, deals with the respiratory system. It usually involves patients who require intensive care including life support and mechanical ventilation. Doctors of this field usually are knowledgeable in diseases and conditions of the chest, such as pneumonia or asthma. Doctors in this field tend to perform minor procedures in surgery of the respiratory tract. Pulmonary specialists often practice critical care medicine. They also manage complicated chest infections.