This thesis describes a combined theoretical and experimental study of the fluid dynamics and heat transfer in a rotating cylindrical c~vity. Experimental results were obtained using a cavity comprising two discs of 762mm diameter, separated by an axial gap up to 152mm, and a peripheral shroud. The cavity was rotated up to 2200 rev/min and cooling air was used, in either an axial throughflow or a radial outflow mode, to cool the heated downstream disc of the cavity. Flow visualisation r~vealed the presence of vortex breakdown for the axial throughflow case and revealed four regimes of flow in the radial outflow case. LDA measurements, made during radial outflow, compared well with the results predicted from approximate solutions of the laminar and turbulent boundary layer equations. For the axial throughflow case, a number of heat transfer tests were conducted with different inlet and outlet conditions and some correlations were obtained for the mean Nusselt numbers. For the radial outflow case, four regimes of heat transfer were identified, and correlations of the mean Nusselt numbers were obtained for each regime. In particular, the results for regime II (the 'Ekman layer regime')agreed closely with the approximate boundary layer model, and the results for regime IV (the 'free convection regime') were consistent with those obtained for the axial throughflow case