We demonstrate first experimental evidence of polarization switching in Stranski-Krastanov (SK) and submonolayer (SML) quantum dot (QD) vertical-cavity surface-emitting lasers (VCSELs). In the case of a SMLQD VCSEL polarization switching is accompanied by polarization mode hopping and is associated with a change of linearly polarized light to elliptically polarized one, hence switching takes place between elliptically polarized states. Current-modulation measurements show that the polarization switching is of thermal origin. Exponential decrease of the dwell time with the pump current has been demonstrated as opposed to exponential increase observed in quantum well (QW) VCSELs when polarization mode hopping takes place between orthogonal, linearly polarized states. In the case of SK-QD VCSELs single polarization switching events stimulated by the increase of the wafer temperature have been observed. After the single switching event the polarization of light remains stable at any wafer temperature and pump current while its direction is perpendicular to that before switching. We will furthermore show preliminary theoretical results on the nonlinear dynamics of a QD laser subject to optical injection, paying particular attention to the influence of the linewidth enhancement factor and the intradot transition time-scales.