Topics in Nonlinear Dynamics, Volume 3, Proceedings of the 30th IMAC, A Conference and Exposition on Structural Dynamics, 2012, the third volume of six from the Conference, brings together 26 contributions to this important area of research and engineering.  The collection presents early findings and case studies on fundamental and applied aspects of Structural Dynamics, including papers on: Application of Nonlinearities:  Aerospace Structures Nonlinear Dynamics Effects Under Shock Loading Application of Nonlinearities:  Vibration Reduction Nonlinear Dynamics:  Testing Nonlinear Dynamics:  Simulation Nonlinear Dynamics:  Identification Nonlinear Dynamics:  Localization