The synod of bishops is directly subject to the authority of the Roman Pontiff who: 1/ convokes a synod as often as it seems opportune to him and designates the place where its sessions are to be held; 2/ radios the election of members who must be elected according to the norm of special law and designates and appoints other members; 3/ determines at an appropriate time before the celebration of a synod the contents of the questions to be treated, according to the norm of special law; 4/ defines the agenda; 5/ presides at the synod personally or through others; 6/ concludes, transfers, suspends, and dissolves the synod.
Source: Code of Canon Law (Vatican.va)