The LML boundary layer wind tunnel was built in 1993. The aim was to build a modern world class facility to enable the study of turbulent boundary layers at high Reynolds number with the most advanced measurement techniques. For that purpose, the wind tunnel had a unique 20 m long test section, to allow thick boundary layers to develop (boundary layer thickness is about 30 cm at the end of the test section, compared to a few mm on an aircraft). This allows of course very detailed near wall measurements. Both velocity (±1%) and temperature (±0.2C) are regulated to allow extensive and precise hot wire measurements. The 20m test section is now fully transparent to allow easy setting of any kind of optical measurement.