ASCE 7 Section 1.4 establishes building importance categories. Category I buildings (low risk) include ordinary residences, commercial buildings, and industrial buildings. Category II buildings (standard risk) include most office and retail buildings. Category III buildings (high risk) include hospitals, fire stations, emergency operations centers, and buildings with occupancy exceeding 5,000. Category IV buildings (critical) include essential facilities with critical functions. The importance factor increases design loads for Categories III and IV, requiring stronger design for hospitals and other critical buildings to remain operational after earthquakes.