Stall, surge, and cavitation are all extreme events that are detrimental to the performance of turbomachines. We use sophisticated imaging techniques to look into the complex flow fields to understand the causes of these events. Later, we use advanced flow control techniques to mitigate their effects. Figure 1 shows how casing grooves can help delay the onset of stall, Figure 2 shows the complex vortical structure measured by 3D PIV, and Figure 3 shows an axial waterjet pump experiencing severe cavitation.