Doctor of Sacred Theology (Latin: Sacrae Theologiae Doctor (S.T.D.); formerly Professor of Sacred Theology, Sacrae Theologiae Professor (S.T.P.)), is the final theological degree in the pontifical university system of the Catholic Church.
The degree builds upon the work of the Bachelor of Sacred Theology (S.T.B.) and the Licentiate of Sacred Theology (S.T.L.). Normally, the S.T.B. is earned in three years, provided the candidate has at least two years of undergraduate study of philosophy before entering an S.T.B. program (if not, the S.T.B. will take five years; Sapientia Christiana assumes this to be the normal situation). The S.T.L. is normally earned in an additional two years, and the S.T.D. is earned after the writing, defense and publication of the doctoral dissertation (an additional 2-3 years). At institutions that offer both civil and church doctorates, the requirements of the S.T.D. will usually--although not always--be shaped so that those reading for the award can receive a Th.D. or Ph.D. in the process of meeting the requirements of the S.T.D.
This compares with, for example in North American institutions, the four-year program for a B.A. at many universities, a two-year program for an M.A., and the writing and successful defense of the doctoral dissertation for the Ph.D. or Th.D. (an additional 2-3 years).
The S.T.D., or the Doctor of Canon Law (D.C.L. or J.C.D.), is the preferred qualification for teaching theology or canon law on a Catholic university faculty or for holding certain other posts of administration. In addition, the S.T.D. is usually required for a permanent post on the theology faculty of an ecclesiastical or pontifical university. However, this requirement can be waived if a teacher holds an S.T.L. John Paul II's Sapientia Christiania notes that in the event where a doctorate is non-canonical, "the teacher will usually be required to have at least a canonical licentiate." (SC, Article 17).
In the US, although it may have more stringent entry requirements than a PhD in theology, it is a research degree that is considered by the U.S. National Science Foundation to be the equivalent of a Doctor of Philosophy.
This degree has sometimes been referred to as Sacrae Theologiae Professor (S.T.P.), "Professor of Sacred Theology" even when the individuals holding it were not in fact Professors. Inscriptions survive on several ancient monuments in British churches which use this abbreviation to denote holders of the degree of Doctor of Divinity (D.D.). The practice of denoting this degree as S.T.P. or S.T.D. has now died out.