Abstract: Since the 60s of the last century, the low-speed streaks, high-speed streaks,burst, ejections, sweeps and various vortical structures in turbulentboundary layers were discovered using flow visualization techniques. Thesecoherent structures have significant influences on the skin friction andheat transfer of turbulent boundary layers, and also on the generation ofturbulence kinetic energy. The induced velocities of vortical structuresinfluence the evolution of other coherent structures, thus they are thekernels of the coherent structures in a turbulent boundary layers. Hairpinvortex is generally accepted as the basic structure in a turbulent boundarylayer. There were many papers on hairpin vortex after the 80s. Thegeneration and re-generation of hairpins and other vortices are theessential factor for the self-sustaining of coherent structures in turbulentboundary layers. It becomes one of the hot topics in studies of turbulentboundary layers in the 90s. Burst created by the low speed fluid ejected fromwall region is the most important source for the generation of turbulenceenergy. Conditional sampling is an important technique for measuring thefrequency of burst and the frequency of occurrence of other coherentstructures. Observations using flow visualizations revealed the basicqualitative characteristics of coherent structures, on which many ideas weredeveloped for drag reduction and enhancing heat transfer. After the 80s,multi-hot wire and PIV techniques were developed, which were applied formeasuring the instantaneous flow velocity vector field. The development ofthree-dimensional PIV technique may be a break-through in theexperimental research on coherent structures. In the present paper,discussions are focused on flow visualization, multi-hot wire and PIVtechniques, their advantages and defects, also their contributions totheirinvestigations of coherent structures.