Some key recent achievements in the development of novel saturable absorbers that are based on semiconductor quantum-dot (QD) structures for the passive mode locking of near-infrared lasers are outlined. These are group IV–VI semiconductor nanoparticles (quantum dots) in glass matrices and self-assembled semiconductor quantum dots (group III–V) grown on semiconductor mirrors (QD-SESAMs). The performance of solid-state (Yb3+, Nd3+ and Cr4+-based), Yb-doped fibre and monolithically integrated semiconductor lasers has been described within the context of ultrashort-pulse generation using these types of QD-based modulators. Particular attention has been paid to the nonlinear parameters of the QD-based saturable absorbers that determine the quality of the mode locking in such laser systems.