I summarize here some of our recent contributions to the understanding and applications of semiconductor nonlinear dynamics. Interplay between polarization switching properties of VCSELs and external optical injection/optical feedback/current modulation gives rise to a rich variety of new dynamical phenomena characterized by multimode behavior, bistability, self-pulsing, noise-induced or noise-sustained instabilities. In these configurations control of polarization is possible but also new perspectives can be expected where the dynamical complexity would help for all-optical signal processing. I will conclude with recent theoretical and experimental works on polarization and nonlinear dynamical properties of quantum dot semiconductor lasers.