A procedure is offered forthe analytical derivation ofthe seismic vulnerability of building classes, that is, probabilistic relationships between shaking and repair cost as a fraction of replacement cost new for a categoryofbuildings.Itsimulatesstructural response,damage,and repaircost for thestructuralandnonstructuralcomponents thatcontributemost toconstructioncost,and thenscalesup results toaccount for the components thatwere not simulated.It does so fora carefully selected sample of building specimens called index buildings whose designs span the domain of up to three features that are believed to most strongly influence seismic vulnerability within the building class. One uses moment matching to combine results for theindexbuildings toestimatebehaviourandvariabilityof thebuildingclass.Onecansimulate non-structuralvulnerabilityalonebyignoringdamageandrepaircostforstructuralcomponents.Theworkis written for a structural engineer with a master’s degree, skilled in structural analysis, but not necessarily experiencedinlossmodelling.