The chapter reviews ultrafast dynamics of carrier transfer into InAs/GaAs and InGaAs/GaAs quantum dots of different doping, densities and interlevel energies. Results from theoretical modeling and time-resolved optical studies are discussed. Considered effects include carrier transport in the barriers, capture into the dots and relaxation in the dots. Several carrier capture and relaxation mechanisms, such as longitudinal optical (LO) phonon emission, carrier-carrier scattering, capture through defect states and relaxation through barrier/wetting layer continuum states are analyzed. LO phonon-assisted capture appears to be a rather universal capture mechanism. For the carrier relaxation in doped quantum dots and/or at high carrier densities, the carrier-carrier scattering-assisted relaxation dominates. In undoped dots and low excitation levels, relaxation through LO phonon emission is found to be the relevant process. Whatever the mechanism, the carrier transfer in QD structures is, as a rule, fast, occurring in 1 to 20 ps time range.