Section 301 provides the foundational definitions and scope for all occupancy classifications in the IBC. This section clarifies that the occupancy classification of a building or structure shall be determined by the character of the occupancy and the major function it serves. Buildings with multiple uses must be classified according to the occupancy that predominates, or if no single use predominates, the most restrictive classification applies. The section defines accessory occupancies, which are secondary uses that support the primary occupancy but do not trigger a change in the building's overall classification if they constitute less than 10 percent of the floor area. For example, a small office within a warehouse is an accessory use. The code also establishes requirements for posted occupancy notices that must be displayed in public spaces to inform occupants of the building's occupancy classification and maximum occupant load. Buildings housing multiple distinct uses may be treated as mixed-use buildings with separate areas dedicated to each occupancy, provided fire separation is maintained. The section further clarifies the responsibilities of the building owner and occupant in maintaining the building in compliance with its classified use. Changes in occupancy use require review and approval by the building official, who may require modifications to bring the building into compliance with new requirements.