In what pertains to the designation of members of the presbyteral council: 1/ the priests themselves are freely to elect about half, according to the norm of the following canons and of the statutes; 2/ according to the norm of the statutes, some priests must be ex officio members, that is, members who are to belong to the council by reason of the office entrusted to them; 3/ the diocesan bishop is freely entitled to appoint others.
Source: Code of Canon Law (Vatican.va)