Judicial power is quite simply the power to judge. In the Catholic Church, it is one branch of the power of governance which bishops exercise either personally or through others. By virtue of their episcopal ordination, bishops have the power within their own jurisdiction to resolve controversies and to make binding decisions based on law and fact. What is called "proper ordinary judicial power" belongs to each diocesan bishop and to some other categories of persons legally considered to be on a similar level as a bishop [for example, the priest or bishop who governs a diocese in the interim between two bishops]. This power can be conferred vicariously on others who then enjoy "vicarious ordinary judicial power", such as judicial vicars and judges.
Church Tribunals are established to cover either a single diocese [the territory or jurisdiction of a bishop] or several dioceses. In this latter case, each of the participating bishops agrees that his power, in the judicial matters submitted to him, should be exercised through the Judicial Vicar [or Officialis, in Latin] and other qualified personnel of the Interdiocesan Tribunal. In this way, the Tribunal truly helps those bishops to carry out their responsibilities as shepherds of their dioceses in the often complex area of judicial procedures. The Interdiocesan Tribunal thus contributes in a very practical way to furthering the supreme law of the Church, the salvation of souls (canon 1752 of the "Code of Canon Law", 1983).
Over and above the judicial vicar of the Interdiocesan Tribunal, every bishop nominates a diocesan judicial vicar to exercise judicial power on his behalf, even if he has no diocesan tribunal. It may be, for example, that a bishop decides to reserve a particular case to himself. In such circumstances his diocesan judicial vicar will normally assist him.
Be it at diocesan or at interdiocesan level, a vice-judicial vicar may also be appointed. Other qualified clergy and lay people may be asked to volunteer as judges, defenders of the bond, promoters of justice, assessors and advocates. Auditors [literally "hearers", or persons authorized on an "ad hoc" basis to take down testimony] and notaries are also appointed according to their professional qualifications in order to facilitate the day to day running of the tribunal. Finally, a tribunal may have recourse to appropriate experts [e.g. in psychiatry] in particular cases.