The condition for categories B and C is that a major part of the conference must cover topics from Mathematical Physics.
Applications for category C should be sent to the Secretary. For category C a conference program, including a list of speakers, is needed and the application should be made at least 6 weeks in advance of the conference; a timely application helps to spread the information.
Applications for category B should be sent to the President. The application must be made at least 6 months in advance of the conference and must include a financial plan which details other sources of support. Decisions are made at three monthly intervals on Jan 15, April 15, July 15 and Oct 15; on Jan 15 we decide about the applications which arrived not later than Jan 1, etc.