Responsa (plural of Latin , 'answer') comprise a body of written decisions and rulings given by legal scholars in response to questions addressed to them. In the modern era, the term is used to describe decisions and rulings made by scholars in historic religious law.
In the Roman Empire
Roman law recognised , i.e., the responses and thoughts of jurists, as one of the sources of (written law), along with laws originating from magistrates, from the Senate, or from the emperor.
A particularly well-known and highly influential example of such responsa was the Digesta (or Digests), in 90 books, the principal work of the prominent second century jurist Salvius Julianus. This was a systematic treatise on civil and praetorian law, consisting of responsa on real and hypothetical cases, cited by many later Roman legal writers.
In the Catholic Church
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In the Catholic Church, responsa are answers of the competent executive authority to specific questions (in Latin, , literally "doubts") sent by Catholic bishops to the Holy See. Responsa given by the Pontifical Council for Legislative Texts which are promulgated as authentic interpretation have the force of law as per canon 16 §2 of the 1983 Code of Canon Law. Other responsa cannot have this binding force, but nevertheless possess a high authority.
Some responsa are given in Notitiae, the official journal of the Congregation for Divine Worship and the Discipline of the Sacraments (CDW). The responsa given in Notitiae are, according to the CDW, to be considered only as private responses unless they are published in official legal records of the Holy See.
In Judaism
thumb|1981 responsum of Rabbi [[Shmuel Wosner, Shevet HaLevi, concerning the status of translated works of Torah, in response to a question from Rabbi Shlomo Sztencl]]
In rabbinic literature, the responsa are known as She'elot u-Teshuvot ( "questions and answers"), and comprise the body of written decisions and rulings given by poskim ("deciders of Jewish law"). A modern term, used mainly for questions on the internet, is "Ask the rabbi".
Judaism's responsa constitute a special class of rabbinic literature, to be distinguished from the commentaries (meforshim)—devoted to the exegesis of the Hebrew Bible, the Mishnah, the Talmud—and from the codes of law which delineate the rules for ordinary incidents of life.