The phenomena of stall and surge in axial-centrifugal compressors is investigated through high-response measurements of both the pressure field and the flowfield throughout the surge cycle. A unique high-response forward-facing and aft-facing probe provides flow information. Several axial-centrifugal compressors are examined, both in compressor rigs and engines. Extensive discussion is presented on the differences in axial and centrifugal rotors and their effect on the system response characteristics. The loading parameters of both are examined and data is presented that shows the increased tolerance of the centrifugal stage to instability. The dynamics of the compressor blade response are shown to be related to the transport time of a fluid particle moving through a blade passage. The data presented provides new insight into the dynamic interactions that occur prior to and during stall and surge. In addition, the inception of rotating stall and the inception of surge are shown to be the same phenomena . An analytical dynamic model (DYNTECC) is applied to one of the compression systems and the results are compared to data. The results show that the model can capture the global effects of rotating stall and surge. The data presented, along with the analytical results, provide useful information for the design of active and passive stall control systems.