This book contains selected papers from NSC08, the 2nd Conference on Nonlinear Science and Complexity, held from July 28 to 31, 2008, in Porto, Portugal. It focuses on fundamental theories and principles, analytical and symbolic approaches, and computational techniques in nonlinear physics and mathematics. Topics covered include chaotic dynamics and transport in classical and quantum systems, complexity and nonlinearity in molecular dynamics and nanoscience, 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, and fractional dynamics.