This book contains selected papers of NSC08, the 2nd Conference on Nonlinear Science and Complexity, held 28-31 July, 2008, Porto, Portugal. It focuses on fundamental theories and principles, analytical and symbolic approaches, computational techniques in nonlinear physics and mathematics. Topics treated include ? Chaotic Dynamics and Transport in Classic and Quantum Systems ? Complexity and Nonlinearity in Molecular Dynamics and Nano-Science ? Complexity and Fractals in Nonlinear Biological Physics and Social Systems ? Lie Group Analysis and Applications in Nonlinear Science ? Nonlinear Hydrodynamics and Turbulence ? Bifurcation and Stability in Nonlinear Dynamic Systems ? Nonlinear Oscillations and Control with Applications ? Celestial Physics and Deep Space Exploration ? Nonlinear Mechanics and Nonlinear Structural Dynamics ? Non-smooth Systems and Hybrid Systems ? Fractional dynamical systems