It has been a long tradition of the International Mathematical Union to keep the members of the Program Committees for forthcoming International Congresses secret. The reason for this secrecy was to protect the members of the committee from personal or political pressure from outside. Invitations to lecture at the International Congresses carry such high prestige that individuals or groups have always made efforts to influence the decisions of the committee.
The IMU General Assembly decided at its meeting in Luzern in 1994 to change the policy and asked the President of IMU in the future to announce the Chairman of the Program Committee for the following Congress as soon as the Executive Committee forms such a Committee.
The IMU president has the privilege to choose the PC chair. The IMU Executive Committee appoints all other PC members after discussion with the PC chair. The PC should have at most 12 members. For each section of a forthcoming ICM, the PC chooses the panel chair and panel core members (usually 3-4). Then the core members plus the chair select the rest of the panel (total of about 6-8). Information about program committee and sectional panel members of previouc ICMs can be found via the links below.
The 15th General Assembly in Santiago de Compostela in 2006 approved new guidelines that describe the roles of the various parties (in particular, the Program Committee (PC), the Organizing Committee (OC), and the sectional panels) involved in the preparation of the scientific program of an ICM. The Executive Committee was charged with the task to regularly review and update these PC/OC Guidelines whenever necessary. The current version was endorsed by the IMU EC on November 21, 2007.