dioecesis

Dioecesis is the Latin term for the ecclesiastical territory governed by a bishop or archbishop, usually translated into English as diocese. The word derives from Greek dioikēsis, meaning administration or governance, and entered Latin via ecclesiastical usage.

Historically, dioeceses were originally civil administrative divisions of the late Roman Empire established by Diocletian. The Church later adopted the term to describe the territorial jurisdiction of a bishop as Christianity organized itself according to settled communities. By the Middle Ages the diocese had become the principal unit of ecclesiastical governance, with its own cathedral, parishes, and clergy.

In Catholic practice, a diocese is led by a bishop; larger historical divisions may be grouped into archdioceses led by an archbishop with metropolitan authority over a province, which comprises several dioceses known as suffragans. The diocesan bishop governs doctrine, liturgy, pastoral care, and discipline within the territory; he is assisted by a curia, a vicar general, episcopal vicars or deans, and councils of priests and laypeople. Parishes within the diocese are led by parish priests and religious communities. The structure supports coordination through national or regional bishops’ conferences.

In other Christian traditions, similar territorial jurisdictions exist under different names, such as eparchies in Eastern Christian churches, or archeparchies, with differing canonical structures.