There is a rich literature of seismic vulnerability and fragility functions, only exceeded by the vast need for more. “Seismic vulnerability function” refers here to a probabilistic relationship between seismic excitation (e.g., shaking intensity) and loss (e.g., repair cost) for a particular asset (e.g., a building) or asset class (e.g., a category of buildings). By “seismic fragility function” is meant here a relationship between seismic excitation and the probability of reaching or exceeding some limit state such as collapse. An international, multi-institutional project is developing guidelines to derive vulnerability and fragility functions empirically, analytically, and by expert judgment, and to update existing functions as new information becomes available. We are also creating new vulnerability and fragility functions to illustrate the guidelines, developing new relationships between collapse and fatality rate, and proposing guidelines to rate functions in several quality dimensions. The work is sponsored by the Global Earthquake Model.