After a short review of the general methods of achieving mode-locked laser operation, the discussion concentrates on the case of passive mode-locking. Rate equation techniques applicable to both giant-pulse and quasi-continuous lasers are outlined. For the giant-pulse case, a sophisticated version of the 'fluctuation model' is described, which allows the stochastic features in the mode-locking performance to be examined quantitatively for the first time. Optimization procedures for these lasers are considered. For quasi-continuous lasers, the powerful compression mechanism that is responsible for the efficient generation of subpicosecond pulses in continuous wave (c.w.) dye lasers is described.