The paper reviews results from in situ straining experiments on Al-Pd-Mn single quasicrystals in a high-voltage electron microscope. Slip planes were determined from the orientation and width of slip traces. Dislocations are generated by a specific cross slip mechanism. On some slip traces, dislocations move at two distinctly different velocities. A stress exponent was determined on a single dislocation by observing its displacement under decreasing load. The in situexperiments reveal the behaviour of individual dislocations in a temperature range where the deformation of bulk specimens is strongly affected by recovery.