The research doctorate is the highest earned academic degree in U.S. postsecondary education. It is always awarded for independent research at a professional level in either academic disciplines or professional fields. Research doctorates earned at accredited institutions are not awarded merely for completing coursework, professional preparation, or for passing examinations.

Content of Doctoral Studies
Doctoral studies may begin after completion of a bachelor's, master's, or first professional degree. In some subjects it is the custom to begin a program leading eventually to the doctorate immediately upon receiving a bachelor's or first professional degree, while in others it is still customary to earn a master's degree before enrolling for a doctorate.

Regardless of the entry point, doctoral studies involve three stages of academic work. The first stage involves the completion of preliminary course, seminar, and laboratory studies and the passing of a battery of written examinations, usually called "writtens" or "comprehensives." If successful at this stage the student is permitted to proceed with doctoral studies, called advancement to candidacy. If not, he or she is withdrawn from the program, in some cases with the possibility of earning a master's degree. The first stage is often longer for students that do not already possess a higher degree.

The second stage consists of a set of advanced seminars and consortia during which the student selects a subject for the dissertation, forms a dissertation committee, and designs his or her research. American educators call the doctoral thesis a dissertation to distinguish it from lesser theses. The dissertation committee consists of usually 3-5 senior faculty in the student's research field, including his or her academic adviser. They do not necessarily have to be from the student's own university. Once the student has developed and presented a research design acceptable to his or her adviser and committee, the independent research phases begins.

Independent research and writing the dissertation can take anywhere from one to several years depending upon the topic selected and the research work necessary to prepare the dissertation. When the academic adviser is convinced that the dissertation is of an acceptable standard to put before the dissertation committee, the student delivers it to all committee members and is scheduled for the dissertation defense. The defense consists of an oral examination in depth before the committee and invited guests during which the student must establish mastery of the subject matter, explain and justify his or her research findings, and answer all questions put by the committee. A successful defense results in the award of the degree.

Some doctoral programs may include additional requirements such as fieldwork or practica or evidence of teaching experience and skills. All doctoral programs require that certain technical skills be mastered in the first stage, including mathematical and computer skills, or other specialized professional competencies relevant to the field being studied.

Time to Degree
The number of years required to complete a U.S. research doctorate vary by subject as well as by whether the student pauses during the program or continues straight through to the end. The median time lapse from earning a bachelor's degree to earning a research doctorate, for students remaining registered, is (in academic years):

For Academic Disciplines:
Humanities - nearly 8 and one-half years
Life Sciences - seven years
Mathematics - nearly 7 years
Physical Sciences - nearly 7 years
Social Sciences/Psychology - seven and one-half years

For Professional and Applied Fields:
Business and Management - over 7 years
Education - over 8 years
Engineering - about 6 and one-half years
Other Professions - over 8 years.

The median number of registered years for all fields is just over 7 years. This means that, when added to the average of 4-5 years for a bachelor's degree, U.S. citizens who earn an American research doctorate have spent around 11 or more academic years in school as full-time students and researchers. During that time they are in structured and supervised programs, not on their own, and they do not benefit from government stipends or from any legal privileges permitting them to enjoy protected student status.

Recognized Research Doctorates
The best-known research doctorate title awarded in the United States is the Doctor of Philosophy (Ph.D.). However, there are a number of other doctoral titles that enjoy the same status and represent variants of the Ph.D. within certain fields. All of them have similar content requirements. The U.S. National Science Foundation (NSF) recognizes many degrees as equivalent to the Ph.D. The following are examples of those that relate to the fields of science, technology, engineering, mathematics, computing, and healthcare:

• Doctor of Architecture (D.Arch.)
• Doctor of Applied Science (D.A.S.)
• Doctor of Business Administration (D.B.A.)
• Doctor of Chemistry (D.Chem.)
• Doctor of Environmental Design (D.E.D.)
• Doctor of Engineering (D.Eng.)
• Doctor of Environment (D.Env.)
• Doctor of Engineering Science (D.E.Sc./Sc.D.E.)
• Doctor of Forestry (D.F.)
• Doctor of Geological Science (D.G.S.)
• Doctor of Industrial Technology (D.I.T.)
• Doctor of Library Science (D.L.S.)
• Doctor of Medical Science (D.M.Sc.)
• Doctor of Nursing Science (D.N.Sc.)
  Doctor of Public Health (D.P.H.)
• Doctor of Professional Studies (D.P.S.)
  Doctor of Design (Dr.DES.)
• Doctor of Science (D.Sc./Sc.D.)
  Doctor of Science in Dentistry (D.Sc.D.)
• Doctor of Science and Hygiene (D.Sc.H.)
• Doctor of Science in Veterinary Medicine (D.Sc.V.M.)
• Doctor of Social Work (D.S.W.)
  Doctor of Education (Ed.D.)
• Doctor of the Science of Law (L.Sc.D.)
• Doctor of Rehabilitation (Rh.D.) 

Bear in mind that first-professional doctoral degrees are not research doctorates in those fields. The research doctorate in all such fields is either the Ph.D. or one of the related research doctorates named in the list immediately above. As with master's degrees, the institution awarding the doctorate has considerable discretion as to the titles it uses for degrees, and thus institutional nomenclature may differ even in the same subject.

Note: Some resources in this section are provided by the U.S. Department of Education.