Doctors
Doctor (gen.: doctoris) means teacher in Latin and is a contraction of the Greek , didaktor, teacher, from the verb , didaskein, to teach. It has been used continuously as an honored academic title for over a millennium in Europe, where it dates back to the rise of the university. This use spread to the Americas, former European colonies, and is now prevalent in most of the world. As a prefix  abbreviated "Dr" its primary designation is a person who has obtained a doctorate (that is, a doctoral degree), which is the highest rank of academic degree awardable.  Doctoral degrees may be "research doctorates", awarded on the basis of competency in research, or "taught doctorates" (also called "professional doctorates", because they are invariably awarded in professional subjects), awarded on the basis of coursework and adjunct requirements (if any) successfully completed by the conferee.
In some languages, when addressing several persons of whom each holds a doctor title, one can use the plural abbreviation Dres. (for Latin 'doctores'). E.g., instead of Dr. Miller and Dr. Rubinstein: Dres. Miller and Rubinstein.  In English the alternative "Drs." can be used.  In the present-day United Kingdom, it would be very unusual - and considered slightly facetious - to address people in this way unless they were business partners; practice elswhere in the world may be different.

# Doctor as a noun
Throughout most of the academic world, the term "doctor" refers to an individual who earned a degree such as the Doctor of Medicine, or M.D. (an abbreviation of the Latin Medicin Doctor) or Doctor of Philosophy, or Ph.D. (an abbreviation for the Latin Philosophi Doctor; or alternatively Doctor philosophi, D.Phil., originally from the Greek  , Didaktor Philosophias, meaning Teacher of Philosophy).
The first academic degrees were all law degrees, and the first law degrees were doctorates.  The origins of the doctorate dates back to the ijazat attadris wa 'l-ifttd ("license to teach and issue legal opinions") in the medieval Islamic madrasahs.  The foundations of the first universities in Europe were the glossators of the 11th century, which were schools of law.   The first European university, that of Bologna, was founded as a school of law by four famous legal scholars in the 12th century who were students of the glossator school in that city.  It is from this history that it is said that the first academic title of doctor applied to scholars of law.  The degree and title were not applied to scholars of other disciplines until the 13th century.  And at the University of Bologna from its founding in the 12th century until the end of the 20th century the only degree conferred was the doctorate, usually earned after five years of intensive study after secondary school.  The rising of the doctor of philosophy to its present level is a modern novelty.  At its origins, a doctorate was simply a qualification for a guildthat of teaching law.
The earliest doctoral degrees (theology, philosophy, law, and medicine) reflected the historical separation of all university study into these three fields. Over time the D.D. has gradually become less common and studies outside theology and medicine have become more common (such studies were then called "philosophy", but are now classified as sciences and humanities - however this usage survives in the degree of Doctor of Philosophy).
The Ph.D. was originally a degree granted by a university to learned individuals who had achieved the approval of their peers and who had demonstrated a long and productive career in the field of philosophy. The appellation of "Doctor" (from Latin: teacher) was usually awarded only when the individual was in middle age. It indicated a life dedicated to learning, to knowledge, and to the spread of knowledge.
The Ph.D. entered widespread use in the 19th century at the Friedrich Wilhelm University in Berlin as a degree to be granted to someone who had undertaken original research in the sciences or humanities. From there it spread to the United States, arriving at Yale University in 1861, and then to the United Kingdom in 1921. This displaced the existing Doctor of Philosophy degree in some Universities; for instance, the D.Phil. (higher doctorate in the faculty of philosophy) at the University of St Andrews was discontinued and replaced with the Ph.D. (research doctorate). However, some UK universities such as Oxford and  Sussex (and, until recently, York) retain the D.Phil. appellation for their research degrees, as does the University of Waikato in New Zealand.
In the US, the Sc. D., which was first conferred in North America by Harvard in 1872, is rarer than the Ph.D. However, the Sc.D. degree has long been awarded by leading institutions such as Harvard University, Johns Hopkins University, Massachusetts Institute of Technology, Washington University in St. Louis, etc. At many of these universities, the academic requirements for the Ph.D. and Sc.D. are identical.
Some ability to carry out original research must be documented by producing a dissertation or thesis, often of substantial length. The degree and title "doctor" is often a prerequisite for permanent (or nearly permanent) employment as a university lecturer or as a researcher in some sciences, though this varies on a regional basis. In others such as engineering or geology, a doctoral degree is considered desirable but not essential for employment. In a small but growing number of fields, the doctorate is felt to injure employment prospects by causing 'overqualification' for the job.

## Medical profession
In English-speaking countries, the title doctor is strongly associated with the medical profession.  Most medical practitioners use the title professionally and socially.
- In the United Kingdom and many Commonwealth countries, those training for the medical profession take a five or six year course leading to the degrees of Bachelor of Medicine and Bachelor of Surgery (MBBS and similar abbreviations); the higher postgraduate degree of Doctor of Medicine (MD) is reserved for those who can prove a particular distinction on the field, usually through a body of published work or the submission of a dissertation.  In guidance issued by Who's Who publisher A & C Black, it is noted that in the context of the United Kingdom, "not all qualified medical  hold the  degree" but that "those ... who have not taken  are addressed as if they had."
- A & C Black also note that British surgeons - a designation reserved for those who have obtained fellowships of the Royal College of Surgeons - are addressed as Mr, Mrs or Miss rather than Dr.  This custom has been commented on in the British Medical Journal and may stem from the historical origins of the profession.
- For many years the UK's General Dental Council (GDC) regarded the use of the title doctor by dentists as a disciplinary offence; however on November 14, 1995 the GDC ruled that dentists could use the title doctor thenceforth provided that they did not do so to imply that they held qualifications that they did not possess.
- Speaking in the House of Commons of the United Kingdom on January 19, 1996, health minister Gerald Malone noted that the title doctor had never been restricted to either medical practitioners or those with doctoral degrees in the United Kingdom, commenting that the word was defined by common usage but that the titles "physician, doctor of medicine, licentiate in medicine and surgery, bachelor of medicine, surgeon, general practitioner and apothecary" did have special protection in law.
- In the United States and other countries, the basic medical qualification is the M.D. degree, usually taken following a Bachelor of Science (B.S.) degree.  In terms of course content and learning outcomes, the United States M.D. is broadly the same as the British MBBS qualifications.  Other health-related disciplines such as dentistry use a similar educational framework.
In German-speaking countries the word Doktor refers exclusively to someone with a research doctorate, and is distinct from Arzt, which refers exclusively to a medical practitioner.  An Arzt who holds the Dr. med. degree is addressed as Herr Doktor; an Artz who does not would simply be Herr.

## Legal profession
Academically, law is a doctoral subject in certain countries, the United States and most European countries among them. Centuries ago, lawyers were called "civil doctors" as distinct from the medical doctor and other types.
In the United States, while some lawyers do use the title "Dr.", practising lawyers are typically called "Mr." or "Ms./Mrs./Miss", regardless of whether they possess a Juris Doctor degree or not.  This is a convention of the courts, of litigation and of the legal profession generally.  The title Counselor is often used in courtrooms in the United States.  A judge or justice in the United States is addressed as Judge followed by his or her surname outside the court room. In the court room, he or she is addressed as "your honor".  Practicing lawyers usually are not addressed as "Doctor". An exception is when a lawyer with a doctoral degree is a witness in a proceeding, in which case that person may be addressed "Doctor" in the witness box.
In other countries such as Portugal, and in most South American countries (Brazil, Argentina, Colombia, Peru, and Uruguay), practising lawyers are called "Doctor". In France, Belgium and Quebec, it is common to use the title "Maitre" (literally meaning Master and abbreviated Me). (In Quebec, the title Maitre is used in English as well as French.)
Historically, U.S. legal education followed the British model.  Law was an undergraduate subject and a degree in law was an undergraduate degree, typically the Legum Baccalaureus (LL.B.) or Bachelor of Laws.  This was the basic qualifying degree.  People who wanted to teach in law school, or who wished to add to their knowledge after a few years of practice, would go on from the LL.B. to take the Legum Magister (LL.M.) or Master of Laws.  The terminal degree in the sequence was the LL.D. or Doctor of Laws. This represents the top law degree in The United Kingdom, Ireland, and throughout the Commonwealth.  In the United States however, a course of events led to the LL.D. becoming a merely honorary degree, while law was elevated to a graduate program and its degrees graduate-level degrees. In the USA, unlike the UK and in the Commonwealth generally, all LL.D. degrees are conferred honoris causa as an honorary degree to people of distinction in public life. There is no course of study leading to this degree.
In most cases, an undergraduate degree in the United States is considered a basic foundation in academia, not a professional degree. Engineering is an exception.  Nevertheless, as a general rule, an academic program requiring that the applicant earn an undergraduate degree prior to application for admission is considered a graduate program, and the degree conferred after completing that program is considered a graduate degree. The LL.B. degree, as a Bachelor's degree, is an undergraduate degree equal to a Bachelor of Arts or a Bachelor of Science.  The Juris Doctor degree became the standard legal degree, to reflect both the graduate nature of the training, and a professional standing.
By World War I, students had to complete two years or 60 credits of undergraduate coursework before admission to law school, this is still the rule enshrined in law in the State of California, though ABA-accredited law schools in the state exceed this minimum standard.  Most ABA-accredited law schools require completion of a bachelor's degree for admission to a J.D. or D.Jur. program.
By 1971, the J.D. degree had completely replaced the LL.B. in the American law school. Some schools also issue graduate degrees in law in programs not meant to train lawyers.  Loyola University of Chicago, for example, offers a Juris Magister or Master of Jurisprudence degree in health law, for health law professionals who require a working knowledge of law (e.g., to communicate intelligently with attorneys) but do not need to become attorneys.
The LL.M. is a post-J.D. degree and exists as a specialty for practicing tax, environment, or other specialized areas in American law.  It also exists as a special case in American legal tradition, as a conversion or adaptation of foreign legal training into qualifications to practice in the United States.  Many states, for example, will accept a foreign law degree as a qualification for admission to practice if the degree is supplemented by an LL.M. degree from an American law school.  A few American law schools do not offer any LL.M. programs except LL.M. programmes for foreign-trained students.
Some U.S. law schools offer explicitly post-J.D./LL.M. law programmes with the creation of the Scientiae Juris Doctor or S.J.D. degree (Doctor of the Science of Law) (J.S.D. is also used).  Like the Ph.D., the S.J.D requires scholarly research and the successful completion of a dissertation.
It is interesting to note than in the ABA Journal, November 2006, an article titled "Lawyers Are Doctors, Too" addresses the question of whether or not an attorney in the United States can call him/herself Doctor.  In essence ABA Informal Opinion 1152 (1970) allows those who hold a Juris Doctor (J.D.) to use the title doctor (the article also clarified this right for holders of the LL.M. (Mastsers of Law), but only in the context of such an individual already retaining a J.D. degree (YourABA, September 2007, quoting Informal Opinion 1152.) See also ABA Model Code of Professional Responsibility, Disciplinary Rule 2-102(E).  Under prior ethical rules, the use of the title doctor was prohibited as being self-laudation. Some states prohibit attorneys from using the title doctor without clarification since it might mislead the public into thinking the attorney is a health professional. In all states attorneys must avoid using the title doctor in a manner that might mislead the public, such as advertising where a medical malpractice attorney uses "Doctor" in a manner which could cause the public to believe the attorney is a medical professional with relevant medical experience.
In Germany, about one in eight lawyers has a doctoral degree and most qualify via two state exams which entitle them to be recognised by a chamber (Anwaltskammer) as legal practitioners. A Doctor of Law was historically accorded the same privileges as a baron (including, for example, the privilege of being allowed to use the same hawk as a baron).

# Use of "doctor" as a title of address
Those who possess a doctoral degree are generally entitled to call themselves "Doctor", although restrictions apply in some jurisdictions and some situations (e.g., when it would mislead someone to think that they are licensed physician). Dentists, optometrists, podiatrists, and veterinarians are often called "doctor" as well.
In the United Kingdom, South Africa, Australia, New Zealand, Canada and other areas whose culture was recently linked to the United Kingdom, the title Doctor generally applies in both the academic and clinical fields.  "Registered medical practitioners" usually do not have a doctorate; rather, they have the degree of Bachelor of Medicine (usually also with surgery). Cultural conventions exist, clinicians who are Members or Fellows of the Royal College of Surgeons are an exception. As a homage to their predecessors, the barber surgeons, they prefer to be addressed as Mr, Mrs, Ms or Miss, even if they do hold a doctorate. When a medically-qualified person passes the notoriously difficult examinations which enable them to become a member of one or more of the Royal Surgical Colleges and become "MRCS", it is customary for them to drop the "Doctor" prefix and take up "Mister".  This rule applies to any doctor of any grade who has passed the appropriate exams, and is not the exclusive province of consultant-level surgeons. In recent times, other surgically-orientated specialists, such as gynaecologists, have also adopted the "Mister" prefix. A surgeon who is also a professor is usually known as "Professor" and, similarly, a surgeon who has been enobled, knighted, created a baronet or appointed a dame uses the corresonding title (Lord, Sir, Dame). Physicians, on the other hand, when they pass their "MRCP" examinations, which enable them to become members of the Royal College of Physicians, do not drop the "Doctor" prefix and remain doctor, even when they are consultants. In the United Kingdom the status and rank of consultant surgeons with the MRCS, titled "mister", and consultant physicians with the MRCP, titled "doctor", is identical. Surgeons in the USA and elsewhere may have the title "doctor".
In Italy, all university graduates (after a 3 year course equivalent to a Bachelor degree) receive the title "Dottore"; after earning a second 2-years degree "Dottore Magistrale", and after earning their Ph.D. "Dottore di Ricerca".  Therefore, Italians thus address each other and present themselves as "Dott." or Dr. even if not holding what in other countries is considered a doctorate. This phenomenon may have been caused by Italy's previous lack of a "Ph.D." degree.
In German speaking countries, all holders of doctorate degrees are appropriately addressed as "Dr X" in all social situations. However, those granted PhDs from other countries may find themselves in legal difficulties if they use the term "Doktor" professionally in Germany.
In the Philippines, where titles and names of occupations usually follow Spanish naming conventions (gender-specific terms), the feminine form of "Doktor" is "Doktora", and is abbreviated usually as "Dra."
Many academic, research scientist and practitioners in subjects allied to medicine also use Dr and/or their terminal degree after their last name. (Terminal degrees include Ph.D., Sc.D., Ed.D., or Psy.D.)
EU legislation recognises academic qualifications (including higher degrees and doctorates) of all member states. In Germany, a recent federal law (signed by all Cultural and Educational Ministers in accord with the EU law) confirmed the standardisation of qualifications and  recognised that non-Germans were also entitled to use the title Doctor if they possessed an equivalent and recognised qualification from an EU member state. Until this Federal Law was introduced, there was no recognised mechanism to prevent administrators in private bodies and civil servants in public-funded bodies (such as universities) from automatically discriminating between the qualifications of people with German doctorates compared to holders of doctorates from an EU member state.  The German university bureaucratic practice of using the post-nominal form, "Ph.D." (or equivalent), to distinguish non-German doctorates can be challenged legally as evidence of arbitrary discrimination and prejudice against non-German nationals (academics). All EU citizens are now "legally entitled" to use and be titled (addressed) as  "Doctor"  or "Dr." in all formal, legal and published communications. For academics with doctorates from non-EU member states, the qualification must be recognised formally ("validated") by the Federal Educational Ministry in Bonn. The recognition process can be done by the employer or employee and may be part of the official bureaucracy for confirming professional status and is dependent on individual bilateral agreements between Germany and other countries.
In Hungary the title of Doctor used to become a part of the name and is added as such to personal ID documents. The use of this practice has been significantly declined in the recent years, although legally it is still possible.

## Correct abbreviation of "Doctor"
The switch from "Doctor" to its abbreviated form involves contraction rather than truncation. In British English it is not necessary to indicate a contraction with a full stop (period) after the abbreviation, while the opposite holds true in North American English. This means that while the abbreviation of Doctor is usually written as "Dr" in most of the Commonwealth, it is usually written as "Dr." in North America.
Similarly, conventions regarding the punctuation of degree abbreviations vary.  In the United Kingdom, it is increasingly common to omit punctuations from abbreviations that are not truncations: while the usual abbreviation of "Esquire" is "Esq.", the usual abbreviation for "Doctor of Philosophy" is "PhD".  It is not incorrect to use the fully-punctuated "Ph.D.", though if this pattern is used, it should be used consistently; practice in particular situations may vary, and it is always more correct to be consistent with a local patterns of usage than to deviate from it.

# Honorary doctorates
An honorary doctorate is a doctoral degree awarded for service to the institution or the wider community. This service does not need be academic in nature. Often, the same set of degrees is used as for higher doctorates, but they are distinguished as being honoris causa: in comprehensive lists, the lettering used to indicate the possession of a higher doctorate is often adjusted to indicate this, e.g. "Hon. Sc.D." rather than "Sc.D".  The degree of Doctor of the University (D.Univ.) however is only awarded as an honorary degree.
Who's Who publishers A & C Black note that honorary doctorates are not used in circumstances where they might be taken to imply an academic qualification and advises following the holder's preference when determining whether to address an "honorary" doctor as "Dr."

# Other uses of "Doctor"
- In some regions, such as the American South, "Doctor" is traditionally added to the first name of people (especially men) holding doctorates, where it is used in either direct or indirect familiar address.
- "Doc" is a common nickname or for someone with a doctoral degree, in real life and in fiction  for example, the character "Doc" in Gunsmoke and Doc Holliday. Also, Doc Savage, 'Man of Bronze', a series of young adult pulp fiction paperback books popular among US high school students during the 1960s and 1970s. "Doc" is Marty McFly's nickname for Doctor Emmett Brown in the Back to the Future trilogy.
- In Roman Catholicism and several other Christian denominations, a Doctor of the Church is an eminent theologian (e.g. Thomas Aquinas, also known as the Angelic Doctor) from whose teachings the whole Church is held to have derived great advantage.