Extensive mode-locking investigations are performed in InGaAs/InAs/GaAs quantum dot (QD) lasers. Monolithic mode-locked lasers are fabricated using QD material systems grown by MOCVD and MBE techniques and emitting at 1.1μm and 1.3μm, respectively. The mode-locking performance is evaluated using a variety of laser designs, with various ridge waveguide geometries, cavity and absorber lengths. Passive and hybrid mode-locking are studied and compared in 3.9mm long devices emitting at 1.1μm and operating at a repetition rate of 10GHz. Using 2.1mm long devices emitting at 1.3μm, 18GHz passive mode locking with 10ps Fourier transform limited pulses is demonstrated. This confirms the potential of quantum dot laser for low chirp, short optical pulse generation. Preliminary investigation of the timing jitter of QD passively mode-locked lasers and the behaviour of the QD absorber are also presented. Finally, we report 36GHz passive mode-locking with 6ps optical pulse obtained using 1.1mm long QD lasers emitting at 1.3μm.