Doctoral degrees required for entry into a profession or whose purpose is not exclusively research are referred to as professional doctorates or first professional degrees. These include Medical Doctor, or M.D.; Juris Doctor, J.D.: Chiropractic Doctor, or C.D.; Doctor of Dental Surgery, DDS; and Doctor of Veterinary Medicine, or DVM. These degrees do not necessarily require prerequisite master's degrees, and are often sufficient for certain teaching positions at universities.
The Doctor of Philosophy, or PhD, degree is the traditional doctorate, earned by students who have completed bachelor's and master's degrees. Considered the terminal degree of your formal education, PhDs can be earned in fields of study from poultry science to nuclear engineering, and are generally completed after a course of study and the writing and defense of a doctoral dissertation. The PhD is a teaching or research degree, and is almost always required for tenure-track positions at major U.S. universities.
In addition to the PhD, the U.S. Department of Education lists other degrees considered to be terminal research degrees. These include doctorates in the following fields: Arts, Business Administration, Church Music, Canon Law, Design, Education, Engineering, Fine Arts, Hebrew Letters, Industrial Technology, Juridical Science, Music, Musical/Music Arts, Music Education, Modern Languages, Nursing Science, Philosophy, Public Administration, Physical Education, Public Health, Sacred Theology, Science, Social Work and Theology.
While the degrees are doctoral-level, there is some debate about who should be allowed to affix the title "Doctor" to his name. Persons holding the PhD degree are generally accorded this title, as are most other doctorate holders, especially in academic circles. Holders of the Juris Doctor degree, however, are not generally titled "Doctor," and instead use "Esq." or "JD" after their names. An exception exists in academia, where either the degree holder or institution may insist that the term "Doctor" be used when addressing a professor.