Nonlinear dynamic (response history) analysis is being used increasingly in design practice for the performance-based seismic design of new buildings. In contrast to nonlinear static analysis, dynamic analysis requires more explicit modeling of cyclic response including strength and stiffness degradation as well as special consideration to selection and scaling of ground motions, definition of viscous damping, and other dynamic effects. To help bridge the gap between state-of-the-art in research and practice, the National Institute of Standards and Technology (NIST) has funded a multi-phase project through the Applied Technology Council (ATC) to develop improved modeling criteria and guidelines for nonlinear dynamic analysis. This paper highlights recently developed modeling guidelines and criteria for buildings, including both general modeling requirements as well as models and criteria that are specific to steel and concrete moment frame buildings. The general requirements address analysis and modeling requirements that are common to all material types and systems, including the relationship between modeling requirements and acceptance criteria, and the influence of modeling uncertainties. The steel and concrete moment frame guidelines incorporate the latest research information on modeling those systems. Illustrative examples are also summarized, which were used to demonstrate application of the guidelines.