The Universal House of Justice is elected every five years by the members of every National Spiritual Assembly in the world, meeting as delegates at an International Convention held at the Baha'i World Centre in Haifa. There are no candidates and no campaigning; delegates vote by secret ballot for the nine individuals they judge best qualified, and the nine with the most votes are elected.
The institution is established in Baha'u'llah's own writings and provided for in the will of Abdu'l-Baha, and it holds authority to legislate on matters not explicitly covered in Baha'i scripture. Baha'is regard that legislative authority as divinely guided, while distinguishing it sharply from revelation: the House of Justice may enact and later repeal its own legislation, which the word of a Manifestation of God could not be.
It was first elected in 1963, ending the six year interregnum that followed the death of Shoghi Effendi in 1957, during which the Hands of the Cause of God had jointly guided the Faith. It has been re-elected every five years since without interruption. Peter Smith's reference work on the Faith sets out both the constitutional basis and the electoral procedure in detail.