With time-resolved PIV the temporal evolution and interaction of flow structures can be investigated in detail. Fluid dynamic coupling effects in time and space can be studied. When an high-framing-rate camera is used for PIV one can take advantage of the same high resolution and dynamic range of standard PIV cameras but combined with high framing rates up to several kHz. Dual cavity lasers with kHz repetition rates and pulse energies up to 50 mJ are nowadays available and can be used to illuminate even large areas for air and water applications.