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